I monitor my exchange mail queues regularly. I noticed recently that mails destined for our sharepoint site were no longer being delivered.  The queue log showed an error 452 4.4.2 Mailbox Full. Iam no sharepoint geek,  I struggled to put this error into perspective. It then dawned on me that Exchange does send emails using SMTP, therefore exchange had to pass emails on to another SMTP server. Armed with this information I set out to look for the SMTP server/Application used by Sharepoint. I realized that SharePoint runs on IIS, therefore there was a possibility of the IIS having SMTP Virtual Server. I checked the settings for the virtual server. Below are the settings found.


 Indeed Sharepoint has SMTP Server, and service had a limit defined for it.  To get around this I disabled this setting and restarted SMTP Virtual Server. Email started flowing again.

To disable the SMTP Drop Directory Quota setting

1. Open Internet Services Manager
 a. Expand the local computer node
 b. Expand SMTP Virtual Server node
 c. Select the Domains node under the SMTP Virtual Server node
2. In the right-hand pane, Right-click on the Local (Default) domain name
 in the list of domains
 a. Select Properties
 b. CLEAR the "Enable drop directory quota" checkbox
 c. Click OK


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