Since rev4965:a850f8bae536 the test/test_mailgw.py
the emails will be compared sharper, especially missmatches in the number of the same 
header fields will be found.

After fixing issue2550869 five failures remain in other headers, here is a list:
======================================================================
FAIL: testMultipartRFC822 (test.test_mailgw.MailgwTestCase)

AssertionError: Generated message not correct (diff follows, expected vs. actual):
  FROM: ['"Contrary, Mary" <issue_tracker@your.tracker.email.domain.example>'] != 
['roundup-admin@your.tracker.email.domain.example', '"Contrary, Mary" 
<issue_tracker@your.tracker.email.domain.example>']
  From: ['"Contrary, Mary" <issue_tracker@your.tracker.email.domain.example>'] != 
['roundup-admin@your.tracker.email.domain.example', '"Contrary, Mary" 
<issue_tracker@your.tracker.email.domain.example>']

======================================================================
FAIL: testNewIssueNoAuthorEmail (test.test_mailgw.MailgwTestCase)

  TO: ['chef@bork.bork.bork, mary@test.test, richard@test.test', 'mary@test.test, 
richard@test.test'] != ['mary@test.test, richard@test.test', 'mary@test.test, 
richard@test.test']
  To: ['chef@bork.bork.bork, mary@test.test, richard@test.test', 'mary@test.test, 
richard@test.test'] != ['mary@test.test, richard@test.test', 'mary@test.test, 
richard@test.test']

======================================================================
FAIL: testNewIssueNoAuthorInfo (test.test_mailgw.MailgwTestCase)

  TO: ['chef@bork.bork.bork, mary@test.test, richard@test.test', 'mary@test.test, 
richard@test.test'] != ['mary@test.test, richard@test.test', 'mary@test.test, 
richard@test.test']
  To: ['chef@bork.bork.bork, mary@test.test, richard@test.test', 'mary@test.test, 
richard@test.test'] != ['mary@test.test, richard@test.test', 'mary@test.test, 
richard@test.test']

======================================================================
FAIL: testSecurityMessagePermissionContent (test.test_mailgw.MailgwTestCase)

  TO: ['chef@bork.bork.bork, richard@test.test', 'richard@test.test'] != ['richard@test.test', 
'richard@test.test']
  To: ['chef@bork.bork.bork, richard@test.test', 'richard@test.test'] != ['richard@test.test', 
'richard@test.test']
======================================================================
FAIL: testUnknownUser (test.test_mailgw.MailgwTestCase)

  FROM: ['Roundup issue tracker <roundup-admin@your.tracker.email.domain.example>', 
'Roundup issue tracker <roundup-admin@your.tracker.email.domain.example>'] != 
['roundup-admin@your.tracker.email.domain.example', 'Roundup issue tracker <roundup-
admin@your.tracker.email.domain.example>']
  MIME-Version: ['1.0', '1.0'] != ['1.0']
  From: ['Roundup issue tracker <roundup-admin@your.tracker.email.domain.example>', 
'Roundup issue tracker <roundup-admin@your.tracker.email.domain.example>'] != 
['roundup-admin@your.tracker.email.domain.example', 'Roundup issue tracker <roundup-
admin@your.tracker.email.domain.example>']
  Precedence: ['bulk', 'bulk'] != ['bulk']

----------------------------------------------------------------------
Ran 119 tests in 32.850s
FAILED (failures=5)