I recently updated the firmware on my router for security reasons... But, I wasn't able to carry over the configuration; too much had changed in how the firmware works. I got it all reconfigured, except one thing... I forgot to forward port 25 to my mail server. Was scratching my head for quite a while until I realized my mistake.
I added the forward, and immediately started receiving junk mail again. Y'all, I've never been so happy to receive junk mail in my life! 
#networking #oops