I have a client in the same situation when sending invoices from AR batch.  One time all get sent, the next half get sent and the next time only a few get sent.  When they get the "Mail Delivery Failed..." error they have to figure out which ones actually were sent and retry.

Terry

I have a client in the same situation when sending invoices from AR batch.  One time all get sent, the next half get sent and the next time only a few get sent.  When they get the "Mail Delivery Failed..." error they have to figure out which ones actually were sent and retry.

Terry

Well I still need to know how to fix it.  You too, right?

Dana

Yes.  It would be different if it was consistent but, unfortunately, it is not.

We have had clients with similar issues lately.  It seems Office365 will "throttle" too many SMTP transmissions, and it's a random problem.  For one client, we used Printboss and inserted a delay between each email.  Another client discovered that installing the Stunnel tool (https://www.stunnel.org) on his network fixed it.

I encountered a similar issue at a client with a third party product and found that Microsoft introduced some "speedbumps" for those that have not disabled TLS 1.0 and 1.1. 

 https://techcommunity.microsoft.com/t5/exchange-team-blog/new-opt-in-endpoint-available-for-smtp-auth-clients-still/ba-p/2659652

It too is random in nature so it works sometimes and then doesn't.

Temp fix was for IT to enable Legacy mode in O365.  Third party then investigated further and found they were not using TLS 1.2 when they thought they were and issued a fix.

is going to get worse with Microsoft ending support for Basic authentication in Exchange services and Office 365 on October 1,2022.  Unless Sage release a patch in time and most likely they will only patch current versions , emailing in Sage will stop working wont it?