We upgraded a customer shop from v4.30 to v4.40.3. Now, eMails with attachments (e.g. the "OrderCompleted.CustomerNotification" template) sent from the system get bounced back with the following SMTP Error:
Remote Server returned '550 5.6.11 SMTPSEND.BareLinefeedsAreIllegal; message contains bare linefeeds, which cannot be sent via DATA and receiving system does not support BDAT'
We haven't changed the eMail-Templates nor the eMail server.
We can also confirm, that bevore the upgrade one of the customers got all eMails delivered and the same customer (same eMail address) doesn't get the eMails now.
The only change was the switch from 4.30 (.NET Framework) to 4.40.3 (.NET Core).
So, there must be a change in the way eMails with attachments are handeld in nopCommerce 4.40.x.
For now, only eMails with attachments will not be delivered.
Any clue what we can do to get the eMails working again?
Thank you, Christian