default mail account not used (iOS 8.3)

Hello,

One of our clients using iPhone 6 (iOS 8.3) has an issue that prevents the default account (Exchange) to be used for sending when activating a secondary POP/SMTP account. The POP/SMTP account is used in this case, and should not be, If I am not wrong.

Exchange is the default account.

Would you think that recreating the accounts in a specific order could fix the issue ?

If need be, i can provide additionnal details.

Thanks for any help