One of the problems I encountered when moving to a new hosting company is that the IP addresses had to change, so I had to set up DNSs and stuff, but also, I found out that all my messages to hotmail addresses were been bounced! I had to set up special DNS records (SPF TXT records) but that was not enough. I had to answer a lot of questions from the guys at Microsoft and finally the lifted the block on my new IPs. It meant a lot of emails were lost (not redirected to spam folders, simply and directly deleted forever) and in the process I discovered that I’m sending around 3,000 email messages every day! Wow, that’s a lot of inter-user conversations, automatic reports on possible trades, and admin reports…! 🙂
I also need to implement a system that intercepts bouncing messages and cancels the responsible accounts.