Question : SMTPException: Failure sending mail

Hi

In my asp.net 3.5 web application, I try to send email to multiple persons (almost 100) using for loop.
It works fine when email has no attachment. But, when email contains the large size attachment (300 KB), after sending 25 emails, it gives a smtpexception:"Failure sending mail".

I have tried using different size of attchment files and I noticed that its giving an exception when the email attachment size reached about 7 MB. (total size of the emails sent with attachment).

What should I do to resolve this problem?

Answer : SMTPException: Failure sending mail

Hi

We found that this problem occurs due to the limit of the session size for SMTP server in IIS.  The default size for Limit session size to (KB): is 10240 (10 MB). It is the total size for sending emails for one mail session. So when our application sends email in a loop and the total email size exceeds this limit, it stops. So depending on mail size, you would be able to send x number of mails where x = Limit/Mail Size.
 
Suggested Action:

We can increase the session limit for the session to 50 MB or 100 MB.

This can be done as follows:

1. Start IIS (Internet Information Services).
2. Right click on Default SMTP Virtual Server and select Properties.
3. Select Message tab.
4. There is an option Limit session size to (KB). At present that value for this option has been set to 10240.
5. We can set this value to 51200 (50 MB) or 102400 (100 MB) or anything else as per our requirement.

Thanks.