Symfony version(s) affected: 4.4.2

Description
In

, the header value is set using $header->toString(). This looks wrong to me as $email->getHeaders()->add(new UnstructuredHeader('X-PM-Metadata-emailUuid', '7ebbf720-e280-4f70-ad5c-89729ee708fa')) will produce a header with the whole header line as a value (i.e. X-PM-Metadata-emailUuid: 7ebbf720-e280-4f70-ad5c-89729ee708fa.

The header value should be 7ebbf720-e280-4f70-ad5c-89729ee708fa.

Possible Solution
In this case, does the solution is to use $header->getBodyAsString() to get the value?