My own yunohost-based mail server, an ISP mail box, two university mailboxes (zimbra).

I mainly like that it's FOSS and on F-Droid (no google services for me). I haven't used Gmail in years, but IIRC, no annoying smart replies or features I don't use like gdrive, photos, hangouts... denser UI, reliable notifications, unified inbox, good multi-account support, support for gpg. It generally gets out of the way. My mother asked me to reinstall it after she changed phones.

I could use better support for nested IMAP folders, better search and syncing of said folders. Probably a better config workflows for non techies? Though that's pretty good already.

I would really like it to be easier to customize the sender mail address, as I make extensive use of +aliases, and would have to create a new identity each time.

I use it with Fastmail for my main email + calendar + todos, and I use it with Purelymail[1] for simply emails with no nonsense.

Both accounts, once setup, just behave.

On the groupware front, I use DavX5 and ICSx5 to do to calendar and todo sync to fastmail, and Tasks.org [2] to do the front end for the todos.

For my work accounts, I use the nine email app which lets me authenticate to exchange active sync without needing a work profile on my phone so I can see emails, calendar, todos etc.

[1] purelymail.com

[2] https://tasks.org/

I'm using the old K9 (before the pre-Mozilla redesign saga) with three POP3 accounts on the mail servers of the registars of my domains. I check my mail on my phone, read it, delete the unnecessary messages, eventually download on my computer (Thunderbird) and backup.

The old UI is very good at this worflow and that's why I ended up using K9. The new UI with the unified inbox is bad at it. This K9/Thunderbird? I should download it to understand how it works. Probably like the new UI but who knows.

I use K9 Mail with Migadu.

Feature-wise, nothing really caught my attention compared to Gmail. At the time that I switched, however, K9 Mail was noticeably snappier for me, had no Google Play Services dependency, and weighed about 7MB to Gmail's 50MB (at the time).

> with which email provider are you using it?

My own fully self hosted dns, postfix SMTP and dovecot IMAP over TLS setup. Not something to attempt casually unless you work in network engineering for an ISP and have the motivation to maintain your own MX and email hosting environment for other reasons.

Migadu(mydomains), google(gmail), microsoft (outlook/hotmail)

I use K9 with Fastmail. I don't like how difficult it is to search. It seems to involve some complex process of navigating back through the mailbox (from unified Inbox to the actual Inbox of the server) and then running the search locally and then pressing back some unknown number of times until a "send query to remote server" toolbar button pops up, and then I press it and it runs the search remotely. Since it only caches a small proportion of my inbox, I always want to send the query to the remote server - it's likely that I could find the item by scrolling faster than I could find it by searching if it's in the cache. I'd be happy if that button was in any search view instead of having to do the weird and complex dance.

I am willing to tolerate this issue because I don't search all that often. In general, a buggy FOSS app is better to me than a commercial app because it is unstable at any given time but relatively stable over time, whereas commercial apps tend to be stable at any given time but unstable over time.

I use it on some self-hosted domains (all IMAP) but have used it with Migadu, MXroute, and others.

I generally like it more than FairMail (simpler, fewer options that I seemed to need to set). But I have tried to sell it to other Android users, and not having swipe-delete made all of them give up. I'm fine without it, but would probably adapt to it if it was Thunderbird standard; I use the iOS email app a lot too.

You might consider Aquamail. I found it to be more powerful and configurable than K9 or Kaiten when I was on android.

I'm MXRoute/fastmail/gmail/exchange on the back end for MX service providers.

Using it with Gandi.

I mainly like that it's no-BS, just works, is available on F-Droid, small download, dark theme, import/export for accounts and settings, lots of switches to flip in the settings should I find any of them necessary to use. I expect none of this to change with the Thunderbird rebrand so it's a win for both projects _and_ the users as far as I can see.

I use it with a few different email providers, including fastmail and a self hosted server. Works pretty well for what I need it to do.

The only feature it's missing which hurts is nested folders. All nested folders are displayed in a list structure, rather than a tree, which is a bit of a pain if you use a nested archive (think Thunderbird's Monthly Archive structure).

I use /e/ foundation's Mail, which is a fork of K9. I use it with Posteo. I used Fairemail before, I don't think I miss anything.

I switched back to K9 recently, as OAUTH2 works now. I am using Gmail(IMAP) and Rediffmail(POP3).

Light-weight. Does not add accounts to Android system. Less colours.

I use it for work email. No notifications, it's just a way to read-only and check if anything comes up when I am AFK.

4 self-hosted accounts, but I don't like much the ~new UI because it makes switching account more complex.