I am able to send about 4 or 5 emails successfully and then after trying the next one get a popup "email unable to be sent" with no further information.
I have done a search and find other people with the same problem without a resolution.
When I had a free account that is the way it would act. Sometimes it worked and sometime not.
Now I am paying for an account and sometimes I still have issues. I really shouldn't have paid for it. Will not pay for a 2nd year. Since Pop and IMAP are not free anymore they can take a hike.