Outlook account verification every 10 mails

For more than a month now outlook asks me to verify my account almost every 10 mails that I send and keeps the e-mails I send in the outbox.

This is ok if it happens lets say once a month.

But every day??

This is extremely annoying especially when I send e-mails using my phone. 

Is there a way to disable this feature or do something to stop it from doing it that often?

i have been using this account for almost 10 years now and I don't want to change it but I can not keep using if this problem persists.

Please anyone with experience kindly help me.