simultaneously fetch and send

Expected behavior

While emailing recordings of a class lecture to students for safekeeping I should be able to fetch email from at least one of my accounts, yes?

Actual behavior

Even at 4g speeds of 39 megabits/s upload a 25meg audio file upload seems like a hellbound wait which would be better spent fetching

is there a hidden setting?

also why can i not check multiple IMAP accounts simultaneously?

what is the best movie of all time in the prior decade?

Steps to reproduce

1. compose email to the most politically correct student with attachment
2. click send
3. sending happens, as i can see the activity meter
4. i click the fetch UX button
5. no fetching happens
6. payload smtp connection closes
7. freed to fetch email sequentially from other IMAPS providers

Environment

K-9 Mail version: fdroid 5403 build 23630

Android version: 5

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

first 3 accounts live on a paid managed VPS next to my moralphobia activism website

the rest are free or subscription, and my campus gmail account

Start by reproducing the behavior from the compose/send flow and the fetch UX button using the stated K-9 Mail and Android versions. Trace whether an active SMTP upload blocks IMAP fetching and whether multiple IMAP accounts are processed sequentially; done means sending and fetching can proceed concurrently where supported, with the behavior confirmed in a test or reproducible scenario.