Ok, I had been on the internet for hours searching this problem and tried all the fixes. First, I changed my password. That didn't work, Then, I tried changing ingoing and outgoing Host name, user name, etc. I also tried deleting my account and adding it all over again. Which I did learn in the process that I was unable to enter my hotmail acct. under outlook. I entered it under other and it downloaded again. When I say it downloaded again, I mean that I had it entered prior to my problem. I was able to receive email but I was unable to send it. Well, after hours of frustration, I called Apple and basically he asked me if I followed all the steps that I previously did and it didn't work. Then he recommended that I reset the phone. Well, before you get nervous, you don't lose any info. You press the on/off button (on the right of 6 plus device) with the round button (the one on the front of the phone, bottom) at the same time, until it turns off and it comes right back on and resets. Well, I then checked my device to see if I could forward mail to myself and presto...... it worked. I'm thinking before you try all the previous steps that you go directly to resetting your phone first. I'm pretty sure that's all that needed to be done to solve this problem. Good luck. I really hope that this post may save someone valuable time.