My mail server is Aol and I am no longer able to initiate a new email from my iphone as I have been able to do in the past. I am able to respond to emails sent to me. How do I correct this?

What happens when you tap on the new message icon:

I am having the same problem (with my husband's account), except for an additional problem of not being able to receive mail with the account either. I have done some research, and it looks like part of the problem is the fact that AOL is going to two factor authentication on these accounts. In some of the messaging site (for an IBM-type machine), it says to look for "OAuth2" as the authentication method. I don't see this as an available option, and I'm reluctant to go into the operating system and start tinkering with authentication settings when I have an Apple device, not a Windows-based environment.

Here is a thread where other users discuss how they resolved this→AOL mail error - Apple Community