A lot of ISPs will require authentication when you try to send mail , but only if you're coming in on a connection that does not belong to that ISP. However in your situation this is clearly not the case.

To be honest I'm not really sure what the problem is

, but as you have not had any more feedback there's a couple of settings you might want to check .
Open O.E. and click on tools > accounts > in the "Internet accounts" box click on your account and choose properties > choose the "servers" tab > If the box with the wording "My Server requires authentication" is checked , uncheck it > apply > OK. If this doesn't help you can go back and reverse the changes.
Whilst you're still in the "servers" tab settings , check the outgoing mail ( SMTP ) address is correct.

Sorry i can't be of more help.

Oh..... and have a safe journey .