Symfony version(s) affected

5.4.22

Description

There is an error when generating Subject header containing two spaces. Both spaces got deleted.

From
Balíček k Vaší žádostič.O42300203 právě dorazil
becomes:
Balíček k Vaší žádostič.O42300203právě dorazil

How to reproduce

> (new \Symfony\Component\Mime\Header\UnstructuredHeader('Subject', 'Balíček k Vaší žádostič.O42300203  právě dorazil'))->toString()
= """
  Subject: =?utf-8?Q?Bal=C3=AD=C4=8Dek?= k\r\n
   =?utf-8?Q?Va=C5=A1=C3=AD_=C5=BE=C3=A1dosti=C4=8D=2EO42300203?= \r\n
   =?utf-8?Q?pr=C3=A1v=C4=9B?= dorazil
  """

Two spaces after O42300203 get lost. Both Gmail and https://dencode.com/en/string/quoted-printable decodes resulting encoded subject header as without any space after O42300203.

Possible Solution

No response

Additional Context

No response