Due to the number of Queen's users reporting this problem, departments should be aware of this issue.

In Safari, AdBlock and/or AdBlock Plus browser plugins affect web based mail services. Messages composed in webmail may be returned as undelivered due to being identified as SPAM when AdBlock is enabled.

Users affected by this problem when sending email can Uninstall / Disable AdBlock in Safari OR they can Whitelist the web client url in the plugin.

To white-list a web site, click the AdBlock icon, and select 'Don't run on pages on this domain'. Then click the 'Exclude' button.

Ref:

https://issues.adblockplus.org/ticket/668
http://support.getadblock.com/discussions/problems/10822-adblock-for-safari-
ads-spam-to-the-email-in-outlook