@peopleinside the issue was resolved by commenting out the code block in the function, assertValidAddress() located inside
vendor/swiftmailer/swiftmailer/lib/classes/Swift/Mime/Headers/MailboxHeader.php
I do not know if what I did is the right way to go about it but it works for me and I wish to share it with the group.
Here is the screenshot of the code block in the function that was commented out.