I am unclear what you want. Is it that you want Thunderbird to remember content from previous emails so that it has a suggested recipient for a new email on the subject? That feature is not there, but maybe I am misunderstanding.

I must either type the full recipient address or manually select a contact; unlike other email clients, it does not suggest addresses from previous correspondence.

1. The following steps light be helpful: "Settings" → "Composition" → "Addressing" section → "When addressing messages, look for matching entries in:" → Tick "Local Address Books" to enable autocomplete. → Tick "Automatically add outgoing email addresses to my: ___". to make Thunderbird provide suggestion from previous correspondence.

Please see the attached image.

2. The following link might be helpful: Addressing an Email https://support.mozilla.org/en-US/kb/addressing-email

Please see "Adding recipients from your address book" section in the above link. Quotation from the above section: "Type search words in the address field of your choice, and recipient autocomplete will assist you."

Thanks for getting back to me. From what I can see, the Windows app has that handy e-mail auto-complete, but the Android one still doesn’t. On the newest Android release there’s no sign of it & I still have to type the whole email or pick someone from my contacts. I’d rather not clog up my address book with every address I might ever email, so I’ll just hang on until the Android app catches up with the Windows version.

1. About autocomplete in Thunderbird for Android:

the Windows app has that handy e-mail auto-complete, but the Android one still doesn’t. ... I still have to type the whole email or pick someone from my contacts.

Thunderbird for Android does have autocomplete. The following link might be helpful: Transfer or connect address book to Thunderbird Android https://support.mozilla.org/en-US/questions/1484999#answer-1702948

2. About suggestion from previous correspondence in Thunderbird for Android: I do not think this function is available in Thunderbird for Android.

I believe the issue is that every email address must be saved in your personal address book. Otherwise, you have to type or copy-and-paste addresses each time, which is awkward and frustrating. The Windows version automatically remembers addresses you’ve used before and suggests them for autofill, but the Android app doesn’t. To fix this, the same autofill feature needs to be added to Android.