SMTP send-as is paid authenticated outbound from an approved domain identity. Forwarding alone is not enough because MX only receives. A customer can write to hello@yourdomain.com and still get a reply from you@gmail.com. That gap is send-as. It is not a filter. It is not catch-all. Free has no send-as.
Quick answer for smtp send as
Forwarding answers “can strangers reach this local-part?” Send-as answers “can this local-part leave as itself?” IETF RFC 5321 — Simple Mail Transfer Protocol is the transport for both. The client help for Gmail is Google Gmail Help — Send mail from a different address. Alignment still follows IETF RFC 7208 — Sender Policy Framework (SPF), IETF RFC 6376 — DomainKeys Identified Mail (DKIM), and IETF RFC 7489 — Domain-based Message Authentication, Reporting, and Conformance (DMARC).
This page is the object. How to attach Gmail’s wizard is a different article. How to send low-volume app mail is a different article. If you only needed inbound, stop after the foreign probe. If invoices and support macros must show the domain, you need SMTP.
MailerZ is inbound MX plus paid send-as, operated by Secuno LLC. Envelope MAIL FROM can use SRS. Header From, Subject, Date, Message-ID, body, and MIME are never rewritten. Not Workspace, not IMAP, not an open relay. Unauthorized send is 550 / 550 5.7.1.
Free: 1 domain, 10 aliases, 1 seat, 14-day store, send-as Off, SMTP Off, API Off. Solo $40/year: send-as On, 2,500 outgoing, 20/hour. Starter $8/$80. Business $19/$190. Agency $39/$390. Unlimited $99/$990, 180-day store, 100,000 outgoing. Confirm MailerZ pricing. Limits are not an inbox SLA.
Product scope is on features and send and reply. Setup order lives in the docs. Do not announce branded replies on Free.
The user problem and the decision criteria
Teams buy forwarding, print billing@, and discover replies look like Gmail. Finance is embarrassed. The forwarder did the inbound job. Nobody bought the outbound hop.
The other failure is treating catch-all as a From factory. Unknown recipients can be held or forwarded on a policy. They are not approved senders. MailerZ will not let a guessed local-part leave.
| Job | Forwarding | Send-as |
|---|---|---|
| Receive hello@ in Gmail | Yes, after MX and a named alias. | Not involved. |
| Reply as hello@ | No. | Paid SMTP plus a client identity. |
| Form mail as noreply@ | No. | Paid SMTP from the app. |
| Newsletter to 40,000 people | No. | Wrong product. Use a campaign platform. |
| Watch unknown local-parts | Hold on Free. Forward on paid policy. | Still not a From. |
Header From is what humans read. Envelope return path is what bounces use. Forwarders may rewrite the envelope with SRS so SPF can pass at the destination. That rewrite is not send-as. Send-as is you originating a new message as the domain.
Technical mail flow
Inbound: stranger → their MTA → your MX → MailerZ → destination mailbox. Header From stays the stranger.
Outbound: your client or app → MailerZ SMTP → recipient MX. MailerZ checks plan, identity, and caps. Header From is the approved alias. DKIM is the dashboard selector. SPF includes the sending hop the dashboard published.
If you reply from Gmail without SMTP, the new message originates at Google. Recipients see Gmail. Your MX never saw it. That is why “forwarding works” and “send-as fails” can be true on the same afternoon.
Loops happen when a destination points back at the alias you send as. Do not do that. Destinations are real mailboxes. One delivery layer.
Step-by-step setup and decision path
Write the jobs
Inbound only, or inbound plus branded replies, or inbound plus app mail. Three different plans.
Name the From
Create the alias before you talk SMTP. Exact local-part.
Prove inbound
Foreign mailbox, unique subject, Header From intact, leftover MX gone.
Upgrade if From must travel
Solo is the smallest send-as card. Confirm pricing.
Attach one client or one app
Gmail wizard, Outlook identity, or env values in one service. Not all three on day one.
Probe outward
Second external inbox. History 250. Header From is the alias.
Failure modes and proof
| Symptom | Cause | Proof |
|---|---|---|
| Reply leaves as Gmail | No SMTP identity. | Received Header From. |
| 550 on first send | Free or unmapped From. | Plan gates and alias list. |
| Form “sent” but nobody got it | Plugin toast, not SMTP 250. | History row. |
| Works to yourself | Gmail short-circuit. | Foreign outbound. |
| Mid-month stop | Hourly or monthly cap. | Counters. Not a refund. |
Not SOC 2, not ISO, not HIPAA, not an inbox SLA. Wording on Security. Stored hops in Mailbox — not IMAP.
MailerZ workflow and product boundary
Secuno LLC operates MailerZ at mailerz.net. The desk is mail.mailerz.net. Inbound MX plus authenticated SMTP. Envelope SRS only.
What MailerZ does
- Forward named aliases into Gmail or Outlook.
- Hold or reject unknown mail on Free; paid plans can forward unknowns.
- Send as approved identities on paid plans.
- Record hop evidence.
- Refuse open relay with 550 / 550 5.7.1.
What MailerZ does not do
- Host IMAP or webmail.
- Enable send-as on Free.
- Rewrite Header From.
- Promise Primary tab placement.
- Replace a bulk ESP.
Cost, alternatives, and trade-offs
A suite seat per role buys a store you may not open. A privacy-mask product hides a destination on someone else’s domain. Cloudflare Email Routing is inbound routing — see Cloudflare — Email Routing documentation. ImprovMX is the closest commercial forwarder class; compare live. MailerZ is the delivery layer when you already have an inbox and you need a From you can prove.
| Approach | You get | You give up |
|---|---|---|
| Forwarding only (Free) | Inbound proof, ten aliases. | Any branded outbound. |
| Paid MailerZ SMTP | Send-as, caps, history. | Hosted mailbox, inbox SLA. |
| Suite | Store, admin, Calendar. Quote the vendor. | Per-user cost if Gmail already worked. |
Solo is $40 per year when one domain must send. Count outgoing against replies and forms together. A contact form and a support queue share the same 2,500 on Solo.
The object lesson: two hops, two proofs
People collapse “email works” into one feeling. Mail does not. The inbound hop can be green while the outbound hop does not exist. The outbound hop can 250 while leftover MX still steals a fraction of inbound. Write both proofs on the same sticky note.
Proof inbound: unique subject from a provider that is not the destination, Header From is the stranger, history shows the destination SMTP response. Proof outbound: unique subject from the paid identity to a third mailbox, Header From is the alias, history shows 250. If you only have one of those, you only finished one product.
Plus addressing on Gmail is not a custom-domain From. IETF RFC 5233 — Sieve Email Filtering: Subaddress Extension describes subaddressing. founder+press@brand.com is an unknown recipient on MailerZ unless you mapped it. Do not publish plus tags as send-as identities.
Shared SMTP passwords across clients are how agencies leak one brand into another ticket. Isolate credentials. Offboard means revoke SMTP, not only delete MX.
A plugin that says “email sent” stored a row in WordPress. That is not SMTP. Open history. If there is no hop, the plugin lied politely.
Campaign platforms exist because operational SMTP has hourly caps on purpose. Solo’s 20/hour is a safety rail. If you need a warm-up story, you are in the wrong category. MailerZ will not pretend otherwise.
When this object lesson is closed, the next action is a list: addresses that only receive, addresses that must send. Map the first on Free if you want. Pay for the second. Confirm pricing. Do not let a homepage footer promise replies the plan cannot originate.
Microsoft device SMTP guidance is Microsoft Learn — Send email from a device or app using Microsoft 365 if Outlook is the client. Do not mix those hostnames with MailerZ values. Each hop has one pair.
Leftover MX is still a hard stop on the inbound side while you debug send-as. Split MX makes “sometimes it works” look like SMTP flapping. Clean DNS first. Then argue about From.
Legal hold and eDiscovery are mailbox-suite problems. The 14-day Free store and the 90-day paid store (180 on Unlimited) are recovery windows for hops this layer saw. They are not an archive. If counsel wants an archive, buy an archive.
Field notes for smtp send as
Operators who bookmark What Is SMTP Send-As and Why Forwarding Alone Is Not Enough usually arrive after a customer replied “why did you email me from Gmail?” The useful brief is still boring. Name the store. Name the printed local-parts that must leave as themselves. Name the nameservers that actually answer. Publish one MailerZ MX set. Delete leftover hosts. Probe inbound from a mailbox that is not the destination. Only then attach SMTP send as.
MailerZ remains inbound MX plus authenticated SMTP around Gmail or Outlook. Envelope SRS only. Header From, Subject, Date, Message-ID, body, and MIME stay intact. It is Mail Box portal webmail, not IMAP, not POP, and not an open relay. Unauthorized send is 550 / 550 5.7.1. Free cannot finish send-as: SMTP and API stay off. Solo is $40 per year when the domain From must travel. Starter is $8 or $80. Business is $19 or $190. Agency is $39 or $390. Unlimited is $99/month or $990/year. Confirm the live pricing page. Those numbers are ceilings, not an inbox-placement service-level agreement.
If leftover Google, Microsoft, Cloudflare routing, or registrar MX is still public, stop widening smtp send as. The identity you built never saw that inbound copy. Priority numbers are an order, not load balancing. A higher preference host is idle while a leftover host still accepts mail. Save the old MX set before you delete anything. Check more than one public view because TTL lies.
Catch-all forward is not a send-as feature. Hold unknowns on everyday production. Review the store. Promote a leftover only when a real person used it. Paid forward belongs to a dated cutover. Fan-out of unknowns into two inboxes trains two spam buttons. Plus addressing on Gmail is not a custom-domain unknown policy. MailerZ will not strip plus tags on your domain the way Gmail does on @gmail.com.
Send-as is a second hop. Creating an inbound alias does not approve outbound. Catch-all does not mint a From. Copy the dashboard host, port, and TLS pair together. Set From to an identity you created. Do not paste a Gmail password into a CMS, a cron file, or a ticket. Do not mail SMTP secrets to support. Send a 550 line, a timestamp, and a Message-ID. Rotate if a secret already leaked.
Self-send from Gmail to the same Gmail account can short-circuit. That green result is why people swear forwarding is enough while customers see Gmail on the reply. Use a second provider. Put a unique subject on the probe so delivery history is searchable. If Header From was rewritten by some other forwarder, authentication stories get noisier. MailerZ does not rewrite Header From on inbound.
Agencies should keep smtp send as per client zone. Separate SMTP credentials. Do not pour every client into one catch-all because the spreadsheet got long. Agency plan capacity exists so you can hold more domains and aliases. It does not replace a named list. Offboard means delete MX you own, revoke SMTP, and stop forwarding leftovers into the agency inbox.
A contact form, a Gmail identity, and a cron can share one monthly cap. If the form already burns Solo’s 2,500, human replies 550 and look like a product regression. Split identities or raise the plan. Do not open a refund ticket for a published ceiling. Campaign mail belongs on a campaign platform. MailerZ is not that platform.
WordPress “sent” toasts, SaaS “message queued” banners, and Gmail unsend windows are not SMTP 250. The only outbound proof that belongs on this page is a received copy plus a history row. If you cannot produce both, you do not have smtp send as yet. You have a feeling.
Registrar forwarding toggles often look free and finish none of the send-as jobs: leftover-MX stop, stored failed hops, hold-unknown, authenticated From. They can be fine for a parked personal domain. They are a poor answer for invoices. Read the hop. If you cannot see why a message died, you cannot run a role that must reply.
A second worked pass: print the public list. Circle the local-parts that must send. If you cannot print the list, you are not ready for production unknowns and you are not ready for a bigger alias ceiling. Unlimited aliases as marketing will not save a missing list. Ten named aliases on Free are enough to stop printing a personal Gmail on a homepage. They are not enough to reply as the domain. Grow the send list when a real person must originate, not when a harvest guessed admin@.
A third worked pass: write the last change on a sticky note before you open the dashboard. Nameserver move, leftover MX, new form plugin, contractor laptop, or a registrar forwarding toggle are the usual five. If the sticky note says leftover MX, you do not have a send-as mystery. You have a split. Delete the leftover. Wait for TTL. Probe inbound again. Only then argue about From.
Comparisons only help after both hops are honest. Cloudflare Email Routing is inbound routing. A privacy-mask product hides a destination on a provider domain. A suite hosts mailboxes, Calendar, and admin. Proton-class mailboxes encrypt a store. MailerZ is the delivery layer when you already have Gmail or Outlook and you need a domain route and a domain From you can prove. Cite the other product’s documentation. Do not invent feature parity.
When What Is SMTP Send-As and Why Forwarding Alone Is Not Enough is closed, the next physical action is a lookup and two probes, not another tab. Start free on one domain you can break. Sign in if the zone already lives here. Review quarterly, or sooner after a nameserver move, a plugin swap, or a staff departure. That is how smtp send as stays a runbook instead of an incident.
Worked examples that are not forwarding
A founder receives hello@ in Gmail and answers from the Gmail account. Inbound worked. Outbound never used the domain. The customer files the thread under a personal address and later cannot find “the company email.” Attach Solo, finish Send mail as, probe a third mailbox. That is smtp send as. It is not an MX change.
A WordPress contact form uses the host mail() and shows “message sent.” History is empty. The destination never saw a hop. Point the plugin at dashboard SMTP, map noreply@ or hello@, send one form to a mailbox you do not own. If Header From is still the host, you attached the wrong pair.
An agency copies one SMTP password into six client sites. One site leaks. All six brands must rotate. Isolate credentials on day one. Agency capacity is not a shared secret. Offboard includes revoke, not only a DNS delete.
A support queue replies all day through one identity and hits Solo’s 20/hour. The 550 is the ceiling. Move campaign-like bursts off the hop, or raise the plan. Do not disable AUTH to go faster. Do not open a second unofficial relay.
Outlook users need a manual identity. Interface labels vary by version. Copy from the MailerZ dashboard, not from a Gmail screenshot. Microsoft Support — Add or manage email accounts in Outlook for Windows is account chrome. Microsoft Learn — Send email from a device or app using Microsoft 365 is device SMTP. Neither is a MailerZ hostname.
A homepage that prints support@ and a footer that says “we reply within a day” is a send-as promise. If the plan is still Free, take the sentence down or upgrade. Marketing copy that the hop cannot keep is how smtp send as becomes a trust problem instead of a DNS problem.
Two forwarders in a chain will not add send-as. They add delay and a second rewrite risk. One MX set, one delivery layer, one paid SMTP pair. If a registrar toggle is still on, turn it off after MailerZ MX is exclusive. Dual hops are how “forwarding works in tests” dies in production.
If you only needed inbound this year, stay on Free and stop promising branded replies. If invoices and support macros must show the domain, Solo is the smallest honest card. Confirm /pricing. Probe both hops. That is the whole smtp send as decision. Write it down before MX.
FAQ
What is SMTP send-as, and why is forwarding not enough?
SMTP send-as is authenticated outbound from an approved domain identity. Forwarding only receives. MX gets mail in. SMTP gets the domain From back out. Free has no send-as. Catch-all does not mint a From. Prove inbound first, then attach paid SMTP and send to a second external inbox.
Does this require a new mailbox?
No. MailerZ is Mail Box portal webmail (Inbox, Sent, New email). It is not IMAP or POP. Gmail or Outlook remains the store. Send-as is a hop, not a login. Buy a mailbox seat only when someone needs a hosted archive or a suite.
Will it work with Gmail or Outlook?
Yes. Gmail uses Send mail as with the dashboard SMTP pair. Outlook uses a manual SMTP identity. Interface labels vary. Free cannot send-as on either client.
What DNS records are involved?
Verification TXT, one MX set for inbound, leftover host MX removed, and the SPF, DKIM, and DMARC values the dashboard shows for sending. SMTP port numbers are not DNS.
What should I test before production?
Foreign inbound to the named From, then one outbound through SMTP to a third mailbox. Read Header From and history. Self-send from Gmail to the same Gmail can hide both paths. A 550 on Free is expected.
Key takeaways
- SMTP send-as is outbound. Forwarding is inbound. They are not substitutes.
- Free has no send-as. A 550 on Free is correct.
- Catch-all does not approve a From.
- Header From stays original on inbound. Envelope SRS only.
- Prove both hops from mailboxes that are not the destination.
- Solo $40/year is the smallest send-as plan. Confirm /pricing.
- Caps are shared across clients and apps.
- Not IMAP, not an open relay, not SOC 2, not a bulk ESP.
Conclusion and next action
If you came here to learn what SMTP send-as is, write the two hops on paper. Keep forwarding for receive. Pay for send-as when the printed string must leave as itself. MailerZ does the pair around Gmail or Outlook. It does not replace a suite or a campaign tool.
Next action: map one alias, probe inbound, then decide whether that alias must send. If it must, leave Free and attach one client. If it must not, stay inbound-only and stop promising branded replies.
Ready to separate the hops
Start free with one domain and prove inbound.
Forwarding on Free. Paid send-as when the From must travel. Sign in if the domain is already there.
Review quarterly, or sooner if MailerZ send-as gates or client wizards change. Author: MailerZ editorial, Secuno LLC.