Q: Since installing the latest iOS update (8.4) I can receive email but can't send.

Hello Ggillmore,

Welcome to the Apple Support Communities!

I understand that after a recent update, you noticed that you can receive new email, but not send. In this situation, I would recommend reading over and working through the suggested steps outlined in the attached article below to troubleshoot this issue. 

Get help with Mail on iPhone, iPad, and iPod touch - Apple Support

Have a great day