Add “HELO” field (for Gmail relay)

If…

1. I am using Google Apps,
2. and I have the relay setup correctly but not requiring authentication,
3. and I would like to use my own “From” email address

then I need to add the HELO value to an domain associated with my Google App account.

I verified this by hardcoding $phpmailer->Helo = “<mydomain>”, and it worked;

So, it would be good if this can be a field in the official plugin.