Two iPhones and one email account - only one can send emails

[#1]

My wife and I share the same Plusnet email account.  We recently got iPhones and set up the email details exactly the same on each phone.  Both of us are receiving emails and I can also send emails, but my wife cannot send emails. 
Is there a limit to the number of devices which can send emails on the same account?  Can anyone advise?
Thanks!

[#2]

Welcome to the Community forums.
I'm not aware of any limits which would prevent both devices sending emails. Though you said the email settings are identical are you sure that the failing one doesn't have an errant tick box selected? Are both connected via your home router or is one connecting via a mobile ISP service?