It's fine unless you have many recipients on one particular domain (or one particular MX). Then it'll notice. For example, I recently did an email shot for som

It's fine unless you have many recipients on one particular domain (or one particular MX). Then it'll notice. For example, I recently did an email shot for someone. Of 3936 registered users, 924 are @hotmail.com and 357 are @gmail.com. (these were sent from a server which has built up its reputation over time; I assume there would be a problem with an order of magnitude more emails arriving from a new location)