Use Migma to review an email's creative after you know what the delivery failure actually says. An SMTP 550 reply is a reason to inspect the full provider response, recipient, and sending configuration before rewriting the subject or rebuilding the layout.
This guide is published by Migma for marketing and product teams working with a technical sending owner. It turns a rejection into a useful incident brief and a controlled creative review. Official sources were checked on October 15, 2026. It does not promise inbox placement or offer a universal fix for every 550 response.
Capture the reply before changing the email
Ask the sending owner for the complete response, its enhanced status code when present, the time, the message reference, and the stage at which the failure occurred. Keep sensitive recipient details in the team's approved incident system rather than pasting a raw log into a public document.
The Loops SMTP error guide explains why the number alone is insufficient: a 550 response can accompany an address problem or a policy rejection. Those lead to different investigations. Record the words after the number as well as the number itself.
Do not translate every permanent rejection into “the email address is wrong.” Also distinguish a rejected submission from an email accepted by the sending service and rejected farther downstream. A screenshot of the campaign editor establishes neither event.
Give the failure a working category
Build a small incident note with a proposed category and the evidence supporting it. Treat that category as a hypothesis until the sending owner confirms it. The following examples are a triage aid, not a replacement for provider-specific documentation.
| Observed evidence | Investigation owner | Creative action in Migma |
|---|---|---|
| Reply explicitly describes an unknown recipient | Audience or account-data owner | Keep the approved design stable while the address is checked |
| Reply names a policy or authentication issue | Sending administrator | Preserve a reference version; review creative only if evidence points to it |
| Reply says relay is prohibited | Mail configuration owner | Avoid rewriting the campaign to solve a routing restriction |
| Reply identifies a content or destination concern | Sending owner and designer | Review the specified copy, links, and assets against the approved brief |
Microsoft's 550, 553, and relay-prohibited guidance illustrates that relay restrictions can be part of this error family. Its examples concern particular mail configurations; do not treat them as a current setup recipe for every platform.
Establish how much of the send was affected
Ask whether the failure affected one recipient, a particular receiving domain, one message type, or the whole send. Use the provider's recorded results to answer that question. An unhappy reply from one subscriber is useful evidence, but it is not a measurement of the entire campaign.
For example, imagine a reminder email rejected for one mistyped address while other recipients received it. Rebuilding the template would introduce a second change without resolving the address problem. In a different incident, every message could fail before leaving the sender because of a configuration restriction. The same headline error would hide a different scope.
Write the affected scope and the unknowns separately. If the provider has not returned a final result, label it pending. Do not count a queued request as a delivered message or a delivered message as proof that the inbox displayed it.
Review creative when the evidence points there
Open the approved version in Migma and compare it with what the sending platform actually used. Confirm the destination URLs, visible promises, sender identity shown in the content, and any recent asset changes. A harmless-looking button can still point to an outdated page after a handoff.
Run Email Preflight to inspect the draft's writing, links, and layout. Use the findings as creative review evidence. A passing check does not reverse a provider rejection, authenticate a domain, or guarantee delivery.
Keep the investigation specific. If the provider points to one destination, ask the responsible owner to investigate it. Do not remove required disclosures, disguise the sender, or rotate through unrelated content to evade a restriction. Resolve the underlying issue with the platform's support or sending owner.
When a copy change is justified, keep a short record: the original sentence, the concern, the approved replacement, and the version exported. This makes the creative decision reviewable without turning speculation about filtering into a supposed test result.
Hand off one controlled revision
Use Migma's export options to prepare the reviewed creative for the chosen destination. The sending owner must still confirm the final platform template, recipient eligibility, sender setup, and test route. Exporting a file does not send it.
Ask for a controlled test appropriate to the diagnosed issue. Keep the recipient set deliberately chosen by the responsible team, and record the provider response for that exact version. Do not repeatedly retry a permanently rejected address just because the layout changed.
If several configuration and creative changes are made together, say so in the incident note. A successful later test cannot establish which change fixed the issue. Avoid writing a confident causal explanation when the evidence only shows that the revised setup worked once.
Close with evidence and a useful next action
A helpful resolution note states what failed, the confirmed cause if known, the change made, and the observed result. It also names what remains uncertain. If the cause is still under investigation, keep the approved creative reference and the provider case linked rather than declaring the problem solved.
Feed confirmed design findings into the next Migma brief. A broken destination or unclear sender explanation can become a repeatable review item. Keep authentication, address hygiene, and provider policy decisions with the people who own those systems.
Prepare a reviewed email in Migma when creative work is part of the fix. The useful outcome is a clear message plus a traceable sending result, with each supported by its own evidence. A more attractive template alone cannot explain an SMTP rejection. Stop changing the design once the creative concern is resolved, and let the sending owner validate the operational correction.
Frequently Asked Questions
Does every SMTP 550 error mean the address is invalid?
No. Read the full provider response and enhanced status code when present. The reply may describe an address, policy, relay, or other issue that requires a different owner.
Should I redesign the email as the first fix?
Keep the approved creative stable until the evidence identifies a content or link concern. Address and sending configuration failures need the appropriate operational investigation.
Can Email Preflight guarantee that a revised email will arrive?
No. It provides creative review findings for the draft. Provider acceptance, downstream delivery, and inbox presentation require separate evidence.
What should a useful resolution note include?
Record the full failure, affected scope, confirmed cause if known, exact change, and observed provider result. Label unresolved questions rather than claiming an unproven cause.