Adblock and Webmail
Some e-mails sent through Outlook Web Access (OWA aka Webmail) are getting rejected as undeliverable by our spam filters.
One common cause is Adblock Plus. (Similar issues arise when using the original AdBlock on a Safari browser for Mac users.) Adblock Plus appears to have an unresolved compatibility issue with Outlook Web Access (OWA) that causes it to insert unwanted content into outgoing emails composed with OWA. The problem manifests itself in some unusual ways. For starters, messages composed in OWA bloat up in size, rising by roughly 256K. Recipients of said messages will probably not notice anything unusual, excepting a marked delay in opening the message. The unwanted content is actually a list of URLs that AdBlock Plus would typically block from loading on any given webpage. That list of URLs contains some fairly unsavory links, which is why outgoing messages are being blocked from being sent by the spam filter.
To work around the issue, you can simply exclude the "mail.middlebury.edu" domain on AdBlock, as follows: Instructions for disabling Adblock on a particular website
A similar work around exists for AdBlock on Safari, you can navigate mail.middlebury.edu and click on the AdBlock icon on your browser.Then simply select "Don't run on this page" which will disable AdBlock when using OWA.