issues with multiple recipients, probably has to with spaces

Quite often I have much difficulties with messages with multiple recipients, especially when manually adding these recpients or copy/pasting them. K9 then refuses to send the message, or removes the recipients in the draft message.

Expected behavior

1. Start writing draft message / reply;
2. Add new/additional recipients by either typing the address in full, or by selecting it from the keyboard history or the pop-up from the address book;
3. Seperate the addresses with the semicolumn (;);
4. Finish the message and click send
5. A sent message;

Actual behavior

1 to 4 as above
5. A red exclamation mark stating that the address is faulty.

Quite often, it is unclear to which address(es) this error refers, especially if the total list is long. Why not move these faulty addresses to the end of the list and/or change colour?

Further, it is quite hard to put the cursor on the right spot in order to try to correct the address, if the faulty address is somewhere in the middle of the extensive list of addresses.

Oddly enough, the error sometimes refers to addresses previously copied from a message in K9 itself (by long pressing on the name of the sender). This happens if the address contains a formatted name as well (besides the address). If I remove this recipient and subsequently only type the address (without the name), all goes well.

It also seems that sometime the error appears for the sole reason that apparantly the list of address contains a space. I understand that an address list shouldn't contain spaces, but in the context of selecting addresses from all kinds of sources (documents, apps, websites, etc.) while drafting a message, a space could be easlily inserted (especially because the keyboard software automatically inserts spaces after a comma or semicolumn). Why not simply automatically correct for such unintended spaces in the list?

And probably the most annoying: K9 has the habit of removing recipients when saving draft messages. I would expect all the recipients to stay in place when saving a draft, even if their address is formatted incorrectly. This allows me to launch other apps (e.g. the browser or a document) to check the address, while saving the K9 message as a draft in the meantime. I've already sent many messages to an incorrect number of recipients because of this.

Steps to reproduce

Draft a message with multiple recipients as stated above.

Environment

K-9 Mail version:
5.600

Android version:
8.1.0

Account type (IMAP, POP3, WebDAV/Exchange):
IMAP

Please take some time to retrieve logs and attach them here:

No source files or tests are named. Start by reproducing the multiple-recipient draft flow on K-9 Mail 5.600 with Android 8.1.0 and IMAP, including formatted names and spaces; done should preserve recipients in drafts and make invalid addresses identifiable without preventing valid messages from being sent.