This might have been a problem that arose from not looking very closely at ActionMailer documentation, but on Saturday, we did a deploy that ended up sending our customers emails with a ton of attachments.
So what happened? We were adding the inline attachments in a before_filter. That was fine. Except that we were adding ALL the inline attachments in a before filter, not just the ones that were needed for every email (say our logo). What we actually wanted to do is add the email specific attachments to just the individual methods within our UserMailer. So if our welcome email includes a certain image, we add it using inline attachments right in the method, like so: