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Thunderbird 68.5.0 on MacOS Catalina - can not send emails unless I put re:, etc. at the beginning of the Subject line

  • 9 iimpendulo
  • 1 inayo le ngxaki
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  • Impendulo yokugqibela ngu legvidal

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Is it true that Thunderbird 68.5.0 (64 bit) is not compatible with MacOS Catalina, Ver. 10.15.3? Therefore, TB 68 will not work properly with Mac.

According to the System Requirements for TB 74.0 beta, The latest MAC Operating System Mac OS x 10.14. Will TB beta 74.0 work with MacOS 10.15.3? If not, do you expect Thunderbird to ever work with MacOS Catalina, ver. 10.15.3?

This implies that the issue described below is because TB 68 is not compatible with MacOS 10.15.3.

Outgoing emails using TB 68.5.0, macOS Catalina, and smtp are NOT delivered to recipients without certain letters in the Subject line.

The issue of sending emails which are not delivered has existed since Mid-December 2019.

A friend uses Thunderbird Release 68.5.0 (but it is 32 bit) and is used with a Windows Operating System. They have no problems sending emails. Prior to mid-December 2019 I had no problems sending emails.

Another friend uses Thunderbird Release 68.4.2 (which is 64 bit) and is used with a MacOS version Yosemite 10.10.5. They have no problems sending emails. Prior to mid-December 2019 I had no problems sending emails.

This implies that the issue seems to revolve around the latest release of Thunderbird (starting in mid-December 2019) along with the latest version of MacOS Catalina.

My recipients never had an issue receiving my emails prior to mid-December 2019.

Thanks for your help with this question.

Is it true that Thunderbird 68.5.0 (64 bit) is not compatible with MacOS Catalina, Ver. 10.15.3? Therefore, TB 68 will not work properly with Mac. According to the System Requirements for TB 74.0 beta, The latest MAC Operating System Mac OS x 10.14. Will TB beta 74.0 work with MacOS 10.15.3? If not, do you expect Thunderbird to ever work with MacOS Catalina, ver. 10.15.3? This implies that the issue described below is because TB 68 is not compatible with MacOS 10.15.3. Outgoing emails using TB 68.5.0, macOS Catalina, and smtp are NOT delivered to recipients without certain letters in the Subject line. The issue of sending emails which are not delivered has existed since Mid-December 2019. A friend uses Thunderbird Release 68.5.0 (but it is 32 bit) and is used with a Windows Operating System. They have no problems sending emails. Prior to mid-December 2019 I had no problems sending emails. Another friend uses Thunderbird Release 68.4.2 (which is 64 bit) and is used with a MacOS version Yosemite 10.10.5. They have no problems sending emails. Prior to mid-December 2019 I had no problems sending emails. This implies that the issue seems to revolve around the latest release of Thunderbird (starting in mid-December 2019) along with the latest version of MacOS Catalina. My recipients never had an issue receiving my emails prior to mid-December 2019. Thanks for your help with this question.

Ilungisiwe ngu Wayne Mery

All Replies (9)

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Hello there Legvidal.


We have read your messages. We try to help you.

Yes ,


Yes, the version you mean is not available for you unfortunately.

All versions described in the shown list have the Mostar having problems with sending emails sometimes and sometimes always by clients.

There was a rumor that a certain add-on would be developed for Thunderbird. But it stayed that way and if there is a pestle it again meets requirements that are not available.

Unfortunately, I have to disappoint you on this topic.

But it may be that an add-on can come on time. I can't say when. try to see if it has been released.



Greetings Firefox Volunteer.

Ilungisiwe ngu День сумо

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I've used beta with catalina and we have many catalina users on version 68 with no problems.

> Outgoing emails using TB 68.5.0, macOS Catalina, and smtp are NOT delivered to recipients without certain letters in the Subject line.

You'll need to be more clear

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I've determined that Catalina is INCORRECTLY missing from the beta system requirements page. I've filed a bug report to get that fixed.

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Thanks for your reply, Wayne. Here is some specific information as well as some more general information which may help.

  • Please keep in mind that I do NOT use webmail. I use smtp from my service provider with outgoing port of 465 and Connection security of SSL/TLS. If the people using a TB beta and macOS Catalina are using webmail, then their messages will be delivered just fine. If smtp is used, then the emails will probably not be delivered.

Outgoing emails which have a Subject starting with the following items will post to my Sent folder AND will be delivered to the recipients. Please note that the “:” is required in the Subject line. Without these items at the beginning of the Subject line, the email will be in my Sent folder but will NOT be delivered.

• Re:

• re: (in all small letters). It will automatically change

to Re: (with a capital R) when received

• Ref:
• ref: (in all small letters). It will stay the same

as all small letters when received

• Fwd: 
• fwd: (in all small letters). 

Please see the following questions which I have posted along with the various replies. Please read all the questions and replies for much more detailed information. I've highlighted some of the relevant information below. There are several screen prints in the prior questions.


Link: https://support.mozilla.org/en-US/questions/1280617

  • Question dated 2/24/20 at 12:16 p.m.: Thunderbird sends email but email never received

When I compose an email and send it, Thunderbird shows it as "Sent." However, the recipient never gets it. This issue started in mid-December 2019.

Reply dated 2/25/20 at 6:21 p.m. from Sfhowes, a top 10 contributor:

- If your mail isn't received with other apps, it suggests the problem lies with factors beyond TB or any mail app. If it works with Apple Mail, there's a good chance the problem is with TB.


Link: https://support.mozilla.org/en-US/questions/1281273

  • Question dated 3/4/20 at 8:49 a.m.: Can’t send email since mid-December 2019 using TB 68.5.0, macOS Catalina ver. 10.15.3, and Suddenlink (smtp)

The issue of not sending emails has existed since Mid-December 2019. This issue is still not solved as of Mar 4, 2020.

The “Send” button posts as Sent in my TB folder. NONE of the recipients receive the emails, though.


Link: https://support.mozilla.org/en-US/questions/1281615

  • Question dated 3/9/20: Will a future release of Thunderbird support macOS Catalina 10.15.3?

According to the TB beta releases, it appears that Thunderbird does not support and work with macOS Catalina 10.15.3. Are there plans for it to do so? I currently have that macOS and TB release 68.5.0 (64 bit).

Reply dated 3/9/20 at 2:03 p.m. from Cymo, a top 25 contributor:

Hello there We have read your mail

We try to help you.

https://support.mozilla.org/en-US/kb/installing-thunderbird-on-mac http://write.flossmanuals.net/thunderbird/removing-thunderbird/

- No, unfortunately at the moment there is not worked on an option for this what you ask.

Look a while later to see if any of this software is or will be offered.


Link: https://support.mozilla.org/en-US/questions/1281605

  • Question dated 3/9/20 at 10:42 a.m.: Why are outgoing emails using TB 68.5.0, macOS Catalina, and smtp, NOT delivered to recipients without certain letters in the Subject line?

The issue of sending emails which are not delivered has existed since Mid-December 2019.

If I compose an email with a Subject of Happy Birthday, it will show up in my Sent folder but will not be delivered to any recipients. This is ALL recipients regardless of domain server.

- If I compose an email with a Subject of Re: Happy Anniversary, it will show up in my Sent folder AND will be delivered to any recipients. The difference is the “Re:” at the beginning of the Subject line.


Link: https://support.mozilla.org/en-US/questions/1281778

  • Question dated 3/11/20: Is Thunderbird 68.5.0 (64 bit) compatible with MacOS Catalina, Ver. 10.15.3?

Is it true that Thunderbird 68.5.0 (64 bit) is not compatible with MacOS Catalina, Ver. 10.15.3? Therefore, TB 68 will not work properly with Mac.

Reply dated 3/11/20 at 2:12 p.m. from Cymo, a top 25 contributor:

We have read your messages. We try to help you.

Yes ,

- Yes, the version you mean is not available for you unfortunately.

All versions described in the shown list have the Mostar having problems with sending emails sometimes and sometimes always by clients.

There was a rumor that a certain add-on would be developed for Thunderbird. But it stayed that way and if there is a pestle it again meets requirements that are not available.

Unfortunately, I have to disappoint you on this topic.

But it may be that an add-on can come on time. I can't say when. try to see if it has been released.

Wayne, for some reason you have a different response from Cymo. I don't know what the difference between your experiences is.

I hope the above information will help resolve the issue.

Thanks for your help.

Ilungisiwe ngu legvidal

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I just discovered that my TB updated automatically today to release 68.6.0. The issues discussed above are still accurate. I still can not send emails unless I put re:, etc. at the beginning of the Subject line.

Thanks for any help you can give.

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subject altered to be more accurate. https://bugzilla.mozilla.org/show_bug.cgi?id=1621079

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Wayne, as of April 23, 2020, my TB release is now 68.7.0 (64 bit) with MacOS Catalina Version 10.15.4. The issue with "re:" etc. still exists. It has not been solved. Thanks for your help.

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As of May 5, 2020, my TB release is now 68.8.0 (64 bit) with MacOS Catalina Version 10.15.4. The issue with "re:" etc. still exists. It has not been solved. Thanks for your help.