Send email from notebook getting "SMTPHeloError: (501, b'5.5.4 Invalid domain name....."

Thanks for your try! but finally I need to add this notebook to a pipeline and make it running automatically, so using the VS Code may not help.

And as you said, an invalid domain name may be generated in a Fabric portal, and I had found a same issue in stackoverflow (but it's not in a Fabric notebook) . 

I tried to add the codes it mentioned, and it works, by explicitly setting sender host name in the ehlo command to anything lowercase.

import smtplib
server_365 = smtplib.SMTP('smtp.office365.com', '587')
server_365.ehlo('mylowercasehost')
server_365.starttls()
server_365.ehlo('mylowercasehost')

 what's more, I found another way to write the code in the docs of smtplib, it also works, as follows:

import smtplib
server_365 = smtplib.SMTP('smtp.office365.com', '587', local_hostname='mylowercasehost')
server_365.starttls()