If you are seeing 550 5.1.0 Invalid Sender Domain then this is most likely attributed to your mailing domain missing an MX record. 

The receipient server checks your MX record to make sure you're a real email address and not spam. This does not affect all ISP's however it is in fact a defense mechanism to prevent spam. 

As a rule of thumb your mailing address should always work. This is why an MX check is made. If you need a tool to check your MX record you can try using mxtoolbox.com

Enter your email address and do an MX lookup. If you need to update your MX record you may need to wait 24 hours for propagation before mailing again.
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