Mailbox-provider troubleshooting

Start with the message’s status and the receiving server’s response. A rejection, a temporary deferral, and a message in a spam folder need different checks. SMTP acceptance proves that the receiver accepted the message; it does not prove inbox placement.

Comail records delivery results and feedback that it receives. Providers do not report every complaint or explain every filtering decision. A zero complaint count in Comail is not proof that nobody marked your mail as spam.

Gmail

Postmaster Tools provides sending-domain data when your domain has enough traffic. Verify your domain using Google’s DNS instructions. The relay operator manages checks that require access to the shared sending IPs.

1. Check the SMTP response or bounce details for the affected message.
2. Check authentication and spam-rate data in Postmaster Tools, if available.
3. Compare your traffic with Google’s sender guidelines. Google recommends keeping reported spam rates below 0.1% and avoiding 0.3% or higher.
4. Ask the recipient to check spam and inbox tabs. The Promotions tab is an inbox category, not a rejection.

Comail’s message category controls Comail’s handling, such as unsubscribe behavior. It does not select Gmail’s inbox tab. A Feedback-ID header also does not establish that Gmail sends individual complaint reports to Comail. Gmail feedback-loop onboarding remains separate operator work.

Microsoft (Outlook, Hotmail, Live)

Microsoft provides Smart Network Data Services (SNDS) for sending-IP data and the Junk Mail Reporting Program for complaint reports. Access and report delivery depend on registration; ask the relay operator for current evidence relevant to the affected IP.

1. Read the rejection or deferral code and follow Microsoft’s linked explanation.
2. If the receiver accepted the mail, ask the recipient to check Junk and their mailbox rules.
3. Give the operator the message ID, time, destination provider, and SMTP response when escalating a repeated failure.

Do not infer a provider’s internal spam score from Comail’s status or promise that a new sender will reach the inbox after a fixed number of days.

Yahoo and AOL

Yahoo’s Complaint Feedback Loop is a DKIM-domain registration service that returns complaint reports. Comail can process supported reports, but report receipt depends on the operator’s current registration and the report’s contents.

1. Read Yahoo’s SMTP response for a rejected or deferred message. A temporary rejection leaves the sender responsible for retrying; it is different from acceptance followed by spam filtering.
2. Check the Yahoo sender requirements for authentication and unsubscribe requirements.
3. Ask the operator to investigate repeated pool-wide deferrals. Include the response text and message times.

Proton Mail

Check the message’s original headers and Comail’s delivery result. For mail accepted into a spam folder, the recipient can review the filtering decision in their mailbox.

A return-path on atmos.email does not align with an unrelated member’s From domain under relaxed SPF alignment. Comail’s member-domain DKIM signature supplies the aligned authentication result for DMARC. See DNS records.

Do not assume a missing complaint report proves successful delivery. Check a recipient mailbox you control when testing, and avoid sending test mail to people who did not request it.

When several providers fail

Check recent DNS, authentication, content, and volume changes. Compare the actual response codes before choosing a fix. A shared failure can indicate a sender-side problem, but it does not establish DNS as the cause.

See troubleshooting, bounces, and feedback monitoring.

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