In order to send my mails from my local Sendmail server to external address, I make it connecting to an authentified SMART HOST provided by my ISP.
The sendmail.cf has the following DS line :
DS[smtp.xxxxxxxxx.org]
and the authinfo file contains :
AuthInfo:smtp.xxxxxxxxxx.org "U:authsmtp" "I:[email protected]" "P:ABCDEFGH" "M:LOGIN PLAIN"
This mechanism works as expected with mails without attachment, or emails with attachement < 4M.
The problem is that when I send a mail with a > 4M attachment, the mail is forwarded to the Smart host, but it is stuck in the client's (typically Outlook) outbox. As a result, the mail keeps getting sent, while it is not removed from the outbox manually.
It seems that the mai server and then the smarthost get the whole mail, but the client abandons the transaction as the timeout has been reached.
I can't find a solution to notice the client that the mail has been successfully received by the server, and does not need to be resent, and I really don't know where to start ...