Update Mailkit Version to 4.x.x

[tidan-16]

Describe the solution you'd like Could we get an update of the Mailkit package? it does not support the version 4.x.x

Describe alternatives you've considered I can use the version 2.5.1, but would prefer keeping things up to date.

Is it possible or no?

[tidan-16]

I guess this project is pretty much out of support right?

[jamesmh]

Mailer is not a priority right now for me (maintainer). Feel free to fix it and submit a PR if you feel you get lots of value from using the mailer + MailKit 4.x.x+ 👍