3CX not sending email to only one user.

[Techinnovate Info]

System Overview:

• Version: 3CX v20.0 Update 7 (Hosted on AWS Lightsail)
• Email Method: 3CX SMTP Service (Default/Direct)
• Recipient Provider: Microsoft 365

I am experiencing a persistent delivery failure for one specific user. The issue affects all system emails, including Welcome Emails and Voicemail Transcriptions.

• Other users on the same domain receive all emails, including welcome emails and Transcripts, without issue.
• This specific user receives absolutely nothing from the 3CX system.

Troubleshooting & Behaviour:

We have isolated the issue strictly to this specific email address string through the following tests:

1. If we change the extension's email to her alias, she receives Welcome Emails and Transcripts immediately.
2. As soon as we change the email field back to the original one, delivery stops immediately. Transcripts and Welcome emails vanish.
3. We completely deleted and recreated the extension. The behaviour is identical. it works with any other email address but fails specifically with her primary address.
4. The trace on the receiving tenant is Empty. The emails are not reaching Microsoft's edge servers, whereas emails for other users in the same tenant appear in the trace as expected.

My Questions:

1. How can I fix this specific issue? Since recreating the user didn't work and other users on the same domain are fine, is there a hidden "block list" or cache in the 3CX instance, or an AWS IP reputation I need to clear?
2. How can I prove the email is leaving the server?

 

[KyriacosS_3CX]

Hello,

You can put the server in Verbose logging where more details of the email requests would be capture.

The 3CX SMTP can blacklist some email addresses if for example they were rejecting email at some point. You can reach out to Customer Care that might be able to help resetting that. https://www.3cx.com/contact/

 

[Alphabetic]

Is this a user you've just created? as Kyriacos said - this can happen when the email address wasnt available when the email was sent. Not sure on how long it takes before it will allow a retry. How long has it been?

 

[SteveITS]

how long it takes before it will allow a retry

IIRC, 7 days.

@Techinnovate Info On 365 you could try using plus addressing to appear as a new email, temporarily and easily. user+3cx@domain.