You don't need the Send Later add-on anymore. Send Later is now an inbuilt feature of Thunderbird 78. You'll find the Send Later option under the File menu. In Offline mode, the Send button automatically becomes Send Later.

Thanks ever so much for your reply, Stans.

I had hundreds of emails (2500+) scheduled to send later at particular time/dates and to subsequently send again at various intervals.

All of the emails are still there in Drafts, but they have lost their scheduling instruction.

When working offline, the send button does indeed become send later. But, the email simply pops into the outbox waiting to send as soon as I go back to working online.

There's no option to select a date/time/repeat instruction. << How do I get this function back? (Please forgive me, I can be a bit (IT) dense sometimes.)

Unfortunately, the inbuilt Send Later feature does not offer the scheduling options that the add-on does. Fortunately, the add-on's developer is working on updating it for v78 compatibility and there reportedly is a mostly functional beta version. See https://blog.kamens.us/send-later/ for details on where and how to download and install the v78 compatible beta version.

Thanks Stans - you're a star. I would normally schedule a Thunderbird email reminder to myself to check when the beta becomes fully tested - but, anyway.

I'm not confident when it comes to IT, uninstalling/installing/beta etc.- is there a method of rolling back to a version of Thunderbird in which send later works? (would the scheduling instructions return?) ?Reverting to a restore point? (Windows 10) Or, am I stuck with trying the beta? - and re-scheduling each, and, every, single, email.

I can't say for sure if the scheduling instructions will be restored when you install the beta version or revert to the previous Thunderbird version. There is only one way to find out. For starters, you should make a backup copy of your Thunderbird profile folder. It's simple, just open your profile folder, Quit Thunderbird (this is important) and copy the entire profile folder to a convenient location. This is far more reliable than System Restore in Windows. After that, you can confidently install the beta add-on and see if it's working well enough for your workflow. You also get to contribute feedback to the add-on author and help bring it out of beta. Downgrading Thunderbird is possible, but should be your last resort for when all else fails.

For help with your Thunderbird profile, see Profiles - Where Thunderbird stores your messages and other user data

Hello Stans - I've been thinking (always dangerous)... I'm going to assume the beta version will 'soon' be released as fully tested, and I'll then be able to simply click 'here' to have the send later/scheduling/repeat function back. Even if 'soon' is January 2021, I'll be OK.

I'm not confident in my abilities – but, I've downloaded/saved the .xpi, removed the (incompatible) send later extension/add-on (the send later button extension remains). Restarted. Installed Add-On from file.

Some of each email’s scheduling instruction parameters carried forward – but not completely accurately. The day/date/time was OK, but multiple days/weeks/months become single.

There is indeed a great deal of work to be done to get anywhere near the old scheduling options. It is certainly nowhere near ready to release. Hopefully it’ll be fixed soon.

I’ll to try find how to contribute feedback to the add-on’s author.

Once again, thanks ever so much for your help. Sincerely appreciated. Paul

If you made a backup copy of your profile folder (before the beta add-on inaccurately restored the schedule info), you could go back to Thunderbird 68 and keep using the stable release of the add-on and hold off upgrading to 78 until the add-on is fully upgraded.

Download v68.12.1 from https://archive.mozilla.org/pub/thunderbird/releases/68.12.1/win32/en-US/

Uninstall v78, install v68.12.1 but don't launch it just yet. Restore the backup copy of your profile folder. Right-click on the Start menu button -> Run then type:

thunderbird.exe --allow-downgrade

Then press Enter. This will launch Thunderbird 68 with permission to launch the profile that had been used by v78. That's what the --allow-downgrade command line switch does. Immediately disable automatic updates in Thunderbird's settings (Options). Check if the stable Send Later add-on is working and if the schedule info is correct.

Too late, I'm afraid Stans. I'm too dense to work out how to backup that profile folder, and too impatient to wait for the stable release (probably because I can never understand why a new version also includes a downgrade of functionality).

I'll wait.

Sorry to be a pain - would you be able to show me where I can check for the release of the tested, working version? Cheers.

Tools > Add-ons then search for Send Later. This will show you the Mozilla add-ons repository where stable releases are published, together with compatibility information.

Please forgive me...

I uninstalled Thunderbird - including deletion of all remnants. To start anew. Restarted pc. Installed TB78.4.2 Restarted pc Added Send Later 8.0.16 Restarted pc

However: I can receive emails, but now I'm unable to send emails - I get the "SMTP timed out" message.

Adding SL instructions to draft emails - they don't send (SMTP issue?)

The SL column will not sort in chron order of when they're due to send. The other columns sort as they should.

Minor point - the SL column defaults (narrow column width) to left hand side of the pane - I move it to the right hand side and expand width - because that's how I've always liked it. When I close & reopen Thunderbird, the SL column goes back to LHS (at the wider width).

Where am I going wrong?

The SMTP issue is resolved (new TB had selected a set of initials on the outgoing settings, and it needed to be another set of initials) - I can now send emails.

But, now the scheduled emails still don't send. (or sort correctly)