My biggest (or funniest now!) fail to date was a couple years ago. I was working on a client email that was being sent to the highest spenders and directed to call a specially created concierge line for them. It was a very quick turnaround but we finally sent it out. About 20 minutes after send, we got a call from the client that a bunch of people were calling the help center because of an email. Turns out the number we sent out in the email was a number off and sent these people to a sexy talk line! needless to say the client was pretty angry so we did a very quick apology email and got together for a post-mortem to trace back the problem. Turns out the copy was not fully checked and the wrong number was sent, so we started implementing a step in QA to check any phone numbers that were in any copy sent over from a third party.
Currently I implement a mandatory link to litmus to have someone not involved in the campaign to check over emails, It helps out a ton to have a fresh set of eyes look for things that I may have missed (since i have to do my own QA). I like to refer to pre-litmus days as the "Dark Ages"...I don't know what I would do without it!
Getting a buy-in for me has been about showing the benefits that it will bring to the company or the team. Bringing examples or potential examples of what it could do work especially for the high up people that don't completely understand your job. At my last job I signed up for a litmus trial and sent a couple of the emails i was working on to show my boss the benefit of the software, it sure beat walking around the office and finding each QA person and seeing what email client they had.
so after further looking into it, we've found out that their update inserted forced line breaks after a certain number of characters (including spaces and tabs) in the code after deployment.
so for example if the declaration called for 'Open Sans' it would insert a line break in the middle of the font declaration and break it. I've contacted them and they are working on fixing it! but I appreciate the help :)