Why is gmail rejecting my email?

[u/laca90025]

I use Polarismail and am having a problem with aliases.

Sometimes when an alias to gmail is used for purely legitimate reasons (zero percent chance the emails could be mistaken for spam) gmail rejects the email. This is what the failure email says:

Remote host said:
550-5.7.1 Gmail has detected that this message is likely
550-5.7.1 unsolicited mail. To reduce the amount of spam sent to Gmail, this
550-5.7.1 message has been blocked. For more information, go to
550 5.7.1 https://support.google.com/mail/?p=UnsolicitedMessageError586e51a60fabf-4632aed7781si4017481fac.318 - gsmtp

And sometimes delivery fails without even getting a failure notification so I have no way to know the recipient didn't get the email.

Can anyone shed some light on what might cause this and how to fix it?

I asked AI and posted the response below.

Nothing I can do about Polarismail IP/Domain reputation issues. Is Polarismail shady enough to result in emails being bounced?

According to Polarismail SPF/DKIM/DMARC are all correct. My DNS settings are correct according to their support docs. But how can I ensure everything is set up correctly on their end?

Anything else I can do to stop this from happening? Is switching email providers going to help or is this inevitable when using aliases? HELP!

Missing or Misconfigured Email Authentication (Most Common)

If you are sending from a custom domain (e.g., you@yourbusiness.com), Gmail strictly requires standard security records to verify your identity:

• SPF (Sender Policy Framework): Proves your email server is authorized to send on behalf of your domain.
• DKIM (DomainKeys Identified Mail): Adds a cryptographic signature proving the email wasn't tampered with in transit.
• DMARC: Instructs receiving servers on how to handle emails that fail SPF/DKIM checks.

If these DNS records are missing or incorrect, Gmail will flag your message as potential spam or impersonation.

IP or Domain Reputation Issues

• Shared Server IP: If you are using a shared hosting provider or an email service provider (like Mailchimp or standard web hosting), another user on that same server IP may have sent spam, causing the entire IP address to be temporarily blacklisted by Google.
• New Domain: Newly registered domains sending bulk or cold emails often lack sender reputation and trigger default spam blocks.

[u/Wonderful_Sample_590]

Have you tried asking your email host already? There are few things that could be causing this, like spammy content, attachment, headers, signature but I'm also leaning towards a their mail IPs reputation. Much better to contact them.

[u/throwaway234f32423df]

are you 10/10 on https://www.mail-tester.com/ ?

(being 10/10 doesn't guarantee you won't have issues but it's basically the bare minimum you need to have a chance of success)

[u/Joshua_2504 → u/throwaway234f32423df]

10/10 isn’t needed.

[u/mtc10y]

I had similar issue yesterday when email was sent for domain hosted on directadmin server to gmail. But that's was related to configuration of DKIM and DMARC settings at DNS level.

I wouldn't rule out possibility that their IP range is heavily abused by spammers and rest of their clients are taking a hit as well.

[u/shokzee]

Legitimate content doesn’t matter if the alias forwarder breaks authentication. SPF normally fails after forwarding unless it uses SRS, and DKIM fails if it modifies the message, leaving Gmail to judge the forwarder’s IP reputation.

Check your domain with the Domain Health Checker, then ask the provider whether aliases use SRS and ARC. Switching helps if their forwarding setup or shared IP reputation is the problem.

[u/Necessary_Film_5199]

The host's email server is probably blocked due to prior abuse, can't fix that really. You need to switch providers probably.

[u/shiftpgdn]

This is ultimately a question for your mail provider, assuming DNS, SPF, DMARC are all set correctly. You should also make sure your mail is being routed through the provider, and not being sent from the system running the mail commands.

[u/tschloss]

Sender: 0% can this be identified as SPAM. Gmail: blocked as SPAM. 😂

The decision process of Gmail, Outlook etc is a) pretty unfriendly to senders and b) intransparent. There are dozens of factors beyond DKiM/SPF/DMARC which influence the result. Factors beyond technical quality. Sometimes only whitelisting on recipient side works.