Bug: An attachment with a name which contains dotted characters sent by Thunderbird has an unreadable name part and/or .dat extension when you open it in Outlook 2017/2019
Status: RESOLVED
Priority: --
Resolution: DUPLICATE
Created: 2020-10-13 19:04:58+00:00
Resolved: 2020-10-27 12:37:58+00:00

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.75 Safari/537.36 Edg/86.0.622.38

Steps to reproduce:

The two different preconditions (independent tests) to reproduce the issue:
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Machine (laptop)/platform 1:
1. Microsoft Windows 10 Professional Version 1909 (OS Build 18363.900)
2. Windows regional settings:
  1) Country or region: Estonia
  2) Regional format: Estonian (Estonia)
3. Thunderbird 78.3.2 (32-bit) - fresh install!
4. Microsoft Office Home and Business 2016 Version 2009 (Build 13231.20262 Click-to-Run)
5. E-mail communication used in both Thunderbird/Outlook: POP3/SMTP over SSL/TSL ports 995/465
6. E-mail addresses: two different addresses with the same domain name/service provider

Machine (desktop)/platform 2:
1.  Microsoft Windows 10 Professional Version 2004 (OS Build 19041.508) - with all updates!
2. Windows regional settings:
  1) Country or region: Estonia
  2) Regional format: Estonian (Estonia)
3. Thunderbird 78.3.2 (32-bit) - fresh install!
4. Microsoft Office Home 365 Version (Build 13231.20390 Click-to-Run) - with all updates!
5. E-mail communication used in both Thunderbird/Outlook: POP3/SMTP over SSL/TSL ports 995/465
6. E-mail addresses: three different addresses - two with one domain name/service provider (as platform 1) and one with another domain name/service provider 


Steps to reproduce the issue:
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1. Open and use Thunderbird to write a letter:
  1) Create a file with a name that contains dotted characters (I have tested only with ä and Ü!) which length is longer than 11 symbols (with/without spaces) and size is not empty
  2) Open Thunderbird, attach the created file into a letter and send it to some e-mail address which is accessible by Outlook

2. Open and use Outlook to read a letter:
  1) Open the letter in Outlook 2017/2019 which was sent by Thunderbird


Actual results:

When the letter sent by Thunderbird is opened in Outlook 2017/2019:

1. Recognize that the attachment filename's second part contains unusual characters with a pattern %XX%XX%XX... where XX are numbers

2. Recognize that the attachment filename's readable part is no longer than certain amount of symbols from the start on the filename (I've got results with 16-18 correct symbols in the beginning of the filename)

3. Recognize that the attachment file's extension is sometimes correct and sometimes it has .dat extension - the pattern is not clear (I've got correct/incorrect results with .docx / .pptx files, but only incorrect .dat extensions with .asice / .cdoc files which are signed / encrypted containers created and used by Estonian ID-card software)


Some other related results which may be helpful:

1. The attachments sent by Thunderbird are:
  1) have correct filenames and file extensions if received and looked via browser in webmail client
  2) have correct filenames and file extensions if received and looked in Outlook 2010 (POP3/SMTP / MSO Home and Business 2010 Version 14.0.7258.5000 (32-bit) / Microsoft Windows 10 Professional Version 1909)

2. The attachments sent from gmail.com / outlook.com via browser have correct filenames and file extensions if received and looked in Outlook 2017/2019 (platform 1 / 2)

2. My college informed that the issue remains if older Thunderbird version was tried (I haven't tested it myself)


Expected results:

When the letter send by Thunderbird is opened by Outlook 2017:

1. The correct attachment filenames without unusual characters are expected
2. The correct attachment file extensions are expected