The following image shows just a small selection of the SMTP servers in my prefs.js per the config editor.

The user interface only displays mail.smtpserver.smtp2 entries from the prefs, that being the default account. Or perhaps it is the one I used last.

when I go to set an SMTP server for one of my other accounts (@GMX) I am offered three possible entries, none of them is the correct GMX account.

Mail.smtpservers shows smtp1,smtp2,smtp9,smtp3,smtp4,smtp14,smtp15,smtp13,smtp6,smtp17,smtp5,smtp8,smtp7,smtp10,smtp11,smtp12,smtp16,smtp18,smtp19

And the correct entry for the account mentioned above is smtp15 show above.

All servers I had ever added shows for me.

Had the same problem (WIN 10 x64 Pro desktop). TB dropped all but the default SMTP config profile and my Gmail SMTP profile in the user interface after initial setup and closing the program overnight . The next day after I discovered this I sent some mail using one of the SMTP accounts then its SMTP config profile appeared again in the user interface. A short while later the others did as well. The email account settings will also show the wrong SMTP account profile being selected once it's own SMTP config profile has disappeared from the list in the user interface. This changes back to what it should be if you send mail with the account and it's SMTP config profile re-appears.

I'm new to TB but not to email. I just setup TB for the first time and this occurred, which was rather disconcerting. Perhaps after you've been using it they all stay put, but something does seem a bit wonky in the initial SMTP config profile listing's behavior after initial setup in the very least.

To update this, today that same outgoing servers (SMTP) dialog shows 19 entries. This is probably correct. But I do wonder if the complaints in support about folders just not appearing in lists at random might be pointing to some sort of lazy load that isn't in this new HTML interface we are getting.

After having sent mail out now from all accounts and seeing the SMTP severs all appearing in the user interface list of them again, they have once again all disappeared after shutting down the software and re-launching it. So it does appear that there's an issue of some sort here. Perhaps the user interface list of SMTP servers is erroneously being populated by an intermediary temp file that gets reset after either a shutdown or a period of SMTP server inactivity?

After some further testing I need to somewhat amend most immediate comment... shutting down the software and coming back in right off does not result in any SMTP servers being dropped from the list of them in the user interface. Also, it seems if all the configured SMTP servers are not being displayed in that list, and I edit any settings on any of the email accounts, all the SMTP servers are once again displayed... at least this just happened although I haven't tried repeated testing to see if it holds true every time and is thus repeatable. Given I also do see lag (I have a very fast machine using an SSD) at times in display updates on-screen, perhaps Matt's idea about some type of a lazy load feature causing problems could be the reason for this strange behavior?

I doubt that, am-smtp.xhtml didn't get any significant changes during the cycle.

(In reply to Magnus Melin [:mkmelin] from comment #7)

I doubt that, am-smtp.xhtml didn't get any significant changes during the cycle.

Magnus, please share any ideas you may have as to what may be causing this behavior.

No idea, sorry.

Anyone still seeing this? If you do, check the Error Console (Ctrl+Shift+J) when it happens.

(In reply to Magnus Melin [:mkmelin] from comment #10)

Anyone still seeing this? If you do, check the Error Console (Ctrl+Shift+J) when it happens.

Just did, see this screenshot, it looks a mess!

https://www.dropbox.com/s/72pox8kbat8zo5b/21_12-01_Moz-Tbird-Error-Console.png?dl=0

Those look unrelated. Clear the console before opening the SMTP server settings

Produces only one warning...

Element.releaseCapture() is deprecated. Use Element.releasePointerCapture() instead. For more help https://developer.mozilla.org/docs/Web/API/Element/releasePointerCapture

But still many SMTP servers are missing in the list being displayed even though they are in fact configured and working.

yup, I'm seeing this in Daily, 97.0a1 (2021-12-17). MacOS Intel

see also bug 1742412

Nothing in error console when I open Account Settings, or go to Outgoing Server (SMTP), yet several are missing.

Yesterday only one SMTP server listed. The default. Today after a power outage they are all back.

If we can not reliably get to see what is in the account settings. What validity does any of the IU have. This is a serious issue that appears to be a direct result of the de-xul of account settings. Will the new web base tree actually just loose mails from the list as this one appears to loose random bits of data that should be displayed. This bug makes me very nervous.

Seems somewhat unlikely de-xul would have impacted this in any way, since am-smtp.xhtml, especially the affected region of it, is still rather xul.
We do seem to have some code that pointlessly allows silent failure when building the list of servers. Maybe reworking that a bit could shed some light on matters.

Pushed by mkmelin@iki.fi:
https://hg.mozilla.org/comm-central/rev/8f2577049b2a
Simplify SMTP server list generation to help track down rendering(?) problem. r=#thunderbird-reviewers

I have also seen this error. I have a feeling when this happened, the smtp servers were also missing in the other account settings, like in the main account pane, when you can select the specific smtp server to be used with this account. That could mean the MailServices.smtp.servers is temporarily broken and not returning server objects.
I started getting smtp server sending errors when sending out messages (like timeout when communicating with the server), after which this problem could occur. I am not sure there is a correlation, but this could be investigated.
Yes, the patch does not seem to have functional changes.

When this error happens to someone, go into Tools->Developer tools->Error console and type "MailServices.smtp.servers" into the bottom input field. It will show you the SMTP servers that Thunderbird tracks right now in the proper objects. If it only shows one, there is a backend problem, not UI.

I've tested this wfm with 2 SMTP servers, one existing, one freshly added, also after app restart on 105.0a1 (2022-08-04) (64-bit), Win10 (i.e. with tentative patch of comment 20 present).

Is anyone still seeing this problem and/or has steps to reproduce?

Well that's very odd. I was going to add a comment saying it was indeed fixed, as I noticed the commit and checked then.

But I just checked again now, and I see only one SMTP server listed, despite having several.

If I send an email from an account with a different SMTP server, then re-check, it gets added to the list: I now have two. And again, from another account, now I have three shown.

So it's definitely not fixed for me, sorry. Or something else has made something similar reappear.

Daily 105.0a1 (2022-08-04) (64-bit); MacOS 12.4

This problem previously occurred when I chose automatic configuration of accounts.

I have since installed a few different Linux distributions in virtual machines. To successfully get around this bug, as I added the accounts, this time, I chose to manually configure each account. When completed, all of the SMTP server entries were listed.

I have never been able to consistently reproduce. Sometimes I open the SMTP list, and it is incomplete, mostly it was all there. I am still checking when I use Thunderbird, and have not seen it recently. But I have also been off the computer for most of the last month. Mail bu phone being my life of late.

With the fix for bug 1773123, just appeared in Daily, my SMTP server list is back to normal: all looks good; thanks very much!

Yeah that was the real problem.