Got an odd one......

iPhone 6, running latest iOS, was running perfectly fine until yesterday. 

User has 2 Gmail, an iCloud and an Exchange account setup.

When the user tries to send an email from the phone, quite often it goes into the Outbox and just sits there. After refreshing it multiple times it finally goes.

Dosent matter what account he is sending from. 

I tried adding a secondary SMTP (my personal one) to the Gmail accounts and it just sits there saying "Verifying" and thats it. So i tried setting up my personal email account, and same thing, it just sits there trying to verify the servers etc. (And yes, my servers are up and running quite happily)

Tried via Vodafone 4G and wifi (ADSL) and same thing.

All other apps run fine on the phone (Facebook, Safari etc) so we know there is connectivity there.

Any ideas ?

Last resort will be to backup the phone and factory reset.