sender address rejected by server

Try going into Settings > Mail, Contacts, Calendars > select the account > account name , tap on SMTP (under the 'Outgoing Mail Server' heading) and then try entering your email account and password in the optional boxes and see if it then works

this was advice given to me by another user - not my idea - but it worked for me

Thank you! This was the answer for me!!

I have this problem too and the above method did not solve the problem. Any other options?