In that case, if it's something they need, you can forget about it. If, on the other hand, it's something you need, then you need to treat the e-mail as a remin

In that case, if it's something they need, you can forget about it. If, on the other hand, it's something you need, then you need to treat the e-mail as a reminder that you need to follow up - essentially, another item in your TODO - so it needs to stay in your inbox. Well, I wrote "you need to", but I'm describing what works for me. :) YMMV, obviously.