Sending mail through C# with gmail is not working after deploying to host

Edit: OP Added extra information crucial to answering this question, but I'm keeping the old answer around as it might still help someone

New Answer: This StackOverflow question already answered this question

OldAnswer: As this StackOverflow answer already answered, you changed the Port on the SMTP Server to 587 instead of its default (25) and this requires elevated permissions causing this error change this:

SmtpServer.Port = 587;

to this:

SmtpServer.Port = 25;

and it should work

Note: When using SSL the port needs to be 443