synkEstablish whether the message was delivered
Ask the recipient to check Spam, search the full mailbox, and inspect any rules that move mail. If you received a bounce, preserve its error text and timestamp. If there is no bounce, that alone does not prove that the message reached the inbox.
Record the sender, destination provider, approximate send time, and any delivery reference. Avoid copying confidential message bodies into support requests. A small test message to an address you control is a better starting point than resending sensitive documents.
Check the real sending path
A message from the web inbox and one from your invoice application may take different routes. Test the actual source that is failing. Review its authentication results and confirm that the visible sender address is the one you intended.
Google's sender guidance recommends SPF, DKIM, and DMARC, while also addressing sender behaviour and reputation. Passing authentication is useful evidence, but it does not guarantee that a receiving provider will place a message in its inbox.
References: Google: email sender guidelines
Review what the recipient expected
A quotation requested by a customer is different from a cold bulk campaign. Check whether the person expected your message, whether the subject describes it accurately, and whether links and attachments are necessary. For marketing mail, use an appropriate service and respect unsubscribe requests.
Avoid treating an employee mailbox as an unlimited campaign engine. A sudden burst of unsolicited mail can create problems for the domain and other users. Synk's employee mail and transactional email requirements should be discussed separately, with the relevant sending limits confirmed.
Fix one cause and test again
If a DNS record is wrong, correct the specific issue and allow the updated record to become visible. If only one external provider is affected, gather examples for that provider rather than assuming the entire mailbox is broken. Check whether the recipient has a personal rule or a previous spam decision.
After a controlled fix, send one new test with an identifiable subject and record the result. Domain-health checks are a starting point; they do not measure recipient engagement, inbox placement, or all sender-reputation factors. No email provider can honestly promise that every message will land in every inbox.
- Capture the bounce or delivery evidence for a specific message.
- Test the service that actually sent the failing email.
- Check authentication and the visible sender.
- Confirm the recipient expected the message.
- Retest after one relevant change and keep the result.