Outgoing email for icloud+ custom domain emails

[jordo6929]

Howdy! We use iCloud Custom domain emails to host our company email. It has previously been working fine, although it seems something recently broke and we are getting Error 500 Unknown Error when trying to send outgoing mail. Incoming mail is working fine as expected.

Here is what I am getting when I try to send an email (from error log)

[2024-08-08 19:18:16] ERROR: Email sending error: 5.1.1 Mailbox does not exist
[2024-08-08 19:18:16] WARNING: Email sending:unknownError; 0
[2024-08-08 19:20:28] ERROR: Email sending error: 5.1.1 Mailbox does not exist
[2024-08-08 19:20:28] WARNING: Email sending:unknownError; 0
[2024-08-08 19:21:23] ERROR: Email sending error: 5.1.1 Mailbox does not exist
[2024-08-08 19:21:23] WARNING: Email sending:unknownError; 0

Has anyone experienced something like this?

[Vadym]

Hi jordo6929,

Please provide related screenshots to get more details.