Hello Swetajoshi you can try this
Go to Settings>Mail, Contacts, Calendars>your email account>account name, tap on SMTP (under the 'Outgoing Mail Server' heading) - tap on your Primary Server and enter your username password - even of It says that it is optional - enter the information anyway. or you can check this post, i found this post on the internet, hope this will help you.
Thank You.
