Investigate if we're sending emails correctly

[jonasfj]

Should we use: content-transfer-encoding quoted-printable

Are we use using any encoding :D

[sigurdm]

We have seen emails end up in the spam folder - that is also worth investigating IMO.

[jonasfj]

Could be related to https://github.com/dart-lang/pub-dev/issues/7833

[isoos]

I think package:mailer uses base64 encoding for everything, and it should be just as good (or better) than quoted-printable. The spam classification is very likely because of the line length issue mentioned in the #7833.