UTF8 in header / suspicious characters in header / mails rejected

[birdmedia]

Hello,

I’m using swiftmailer as part of Contao CMS where it is implemented for the mailing/newsletter system.

I discovered that in cases where there are special characters (German Umlaute) used in the header, some recipients refuse to accept these mails because of “suspicious characters in header”.

Example header: Anfrage zu Ihren =?UTF-8?Q?Akti?=\015 =?UTF-8?Q?vit=C3=A4ten?= („Aktivitäten“ would be correct)

Is this a kind of bug in the UTF8 encoding of swiftmailer? How to solve this problem?

[neufeind]

Could you maybe see if the fix in issue #393 helps here?