Custom header supports

Useful features for example when working with mail automation tools that allow unsubscription management on a finer level with tags (Mailgun for example).

Thank @TristanPouliquen 🎊

Remove FosUser dependency

Merge pull request #10 from AppVentus/unlink-fos

remove FosInstantMail

Symfony v3 support

Merge pull request #9 from BFoucher/master

update yml for symfony3 compatibilty

Avoid circular be passing doctrine outside the construct

Merge pull request #6 from Charlie-Lucas/master

:bug: remove attachment uploader service doctrine dependency

1.0.0: Merge pull request #5 from Charlie-Lucas/master

Save Attachments on server