SMTP; 553 5.1.8
Last week we started getting complaints from customers that they were not getting our emails. Reviewing server logs we found that half the emails going out are bouncing with the error
SMTP; 553 5.1.8 <[email scrubbed]>... Domain of sender address [email scrubbed] does not exist
Nothing has changed on our part, the complaints started on 11/08/2023.
The odd thing is if I send the emails again they seem to have the same 50/50 chance of going through or bouncing again with the same error.
This is only impacting emails sent to att.net and bellsouth.net, and then only half of them. All other emails to other domains are going out fine.
Anyone else run into something similar. I can't find resources on AT&T's postmaster page for this type of message.