STEPS TO REPRODUCE
1. Connect trojita to a corporate Google domain with an app password
2. Click on the Important folder

OBSERVED RESULT
Error dialog, IMAP connection killed.

EXPECTED RESULT
IMAP connection is not killed.

SOFTWARE/OS VERSIONS
NAME="Ubuntu"
VERSION="20.04.3 LTS (Focal Fossa)"

Qt Version: 
libqt5core5a/focal-updates,focal-security,now 5.12.8+dfsg-0ubuntu2.1 amd64 [installed,automatic]
libqt5dbus5/focal-updates,focal-security,now 5.12.8+dfsg-0ubuntu2.1 amd64 [installed,automatic]
libqt5gui5/focal-updates,focal-security,now 5.12.8+dfsg-0ubuntu2.1 amd64 [installed,automatic]
libqt5keychain1/focal,now 0.10.0-1build1 amd64 [installed,automatic]
libqt5network5/focal-updates,focal-security,now 5.12.8+dfsg-0ubuntu2.1 amd64 [installed,automatic]
libqt5positioning5/focal,now 5.12.8+dfsg-0ubuntu1 amd64 [installed,automatic]
libqt5printsupport5/focal-updates,focal-security,now 5.12.8+dfsg-0ubuntu2.1 amd64 [installed,automatic]
libqt5qml5/focal,now 5.12.8-0ubuntu1 amd64 [installed,automatic]
libqt5quick5/focal,now 5.12.8-0ubuntu1 amd64 [installed,automatic]
libqt5sensors5/focal,now 5.12.8-0ubuntu1 amd64 [installed,automatic]
libqt5sql5-sqlite/focal-updates,focal-security,now 5.12.8+dfsg-0ubuntu2.1 amd64 [installed,automatic]
libqt5sql5/focal-updates,focal-security,now 5.12.8+dfsg-0ubuntu2.1 amd64 [installed,automatic]
libqt5svg5/focal,now 5.12.8-0ubuntu1 amd64 [installed,automatic]
libqt5webchannel5/focal,now 5.12.8-0ubuntu1 amd64 [installed,automatic]
libqt5webkit5/focal-updates,now 5.212.0~alpha4-1ubuntu2.1 amd64 [installed,automatic]
libqt5widgets5/focal-updates,focal-security,now 5.12.8+dfsg-0ubuntu2.1 amd64 [installed,automatic]
libqt5x11extras5/focal,now 5.12.8-0ubuntu1 amd64 [installed,automatic]

ADDITIONAL INFORMATION

Error dialog:

The IMAP server sent us a reply which we could not parse. This might either mean that there's a bug in Trojitá's code, or that the IMAP server you are connected to is broken. Please report this as a bug anyway. Here are the details:
UnexpectedHere: body-fld-param: string not found
* 33175 FETCH (UID 33505 RFC822.SIZE 4744 MODSEQ (9800684) INTERNALDATE "01-Mar-2015 12:00:11 +0000" ENVELOPE ("Sun,  1 Mar 2015 12:00:07 +0000 (UTC)" "REDACTED" (("REDACTED" NIL "reports" "REDACTED.com")) (("REDACTED" NIL "reports" "REDACTED.com")) (("REDACTED" NIL "reports" "REDACTED.com")) ((NIL NIL "REDACTED" "REDACTED.com")(NIL NIL "reports" "REDACTED.com")) NIL NIL NIL "") BODYSTRUCTURE (("TEXT" "HTML" NIL NIL NIL "8BIT" 430 17 NIL NIL NIL)("MIXED" ("NAME" "REDACTED.csv") ("ATTACHMENT" ("FILENAME" "REDACTED.csv")) NIL) "MIXED" ("BOUNDARY" "ANTIQUEMARKER") NIL NIL) BODY[HEADER.FIELDS (References List-Post)] {2}

Connection Tab:

13:58:13.729 <<< * 34085 FETCH (UID 34415 RFC822.SIZE 4739 MODSEQ (10186843) INTERNALDATE "01-May-2016 12:00:32 +0000" ENVELOPE ("Sun,  1 May 2016 12:00:31 +0000 (UTC)" "REDACTED" (("Cri
(+ 7230 more bytes)
13:58:13.730 UnexpectedHere body-fld-param: string not found␊* 34085 FETCH (UID 34415 RFC822.SIZE 4739 MODSEQ (10186843) INTERNALDATE "01-May-2016 12:00:32 +0000" ENVELOPE ("Sun,  1 May 2016 12:00:31 +0000 (UTC)" "Website perfor
(+ 1592 more bytes)
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 34415:34514 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 28725:28824 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 26128:26147 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 22703:22727,22729:22803 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 21348:21447 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 19664:19673,19675:19736,19739:19766 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 18316:18337,18339:18350,18352:18417 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 16642:16741 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 15637:15736 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 14294:14393 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 13287:13386 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 12283:12382 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 11279:11378 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 10264:10363 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 9594:9693 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 8925:9024 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 8256:8355 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 7240:7339 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 6230:6329 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 5220:5319 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 4215:4314 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 2677:2776 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 1654:1753 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 630:653,655:663,665:668,670:732 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 293:353,355:393 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 3013:3041,3043:3085,3087:3114 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 4885:4984 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 6903:7002 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 9260:9359 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 14967:15066 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 23370:23469 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 49826:49834 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 44908:44988,44990:44995,44997:45009 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 40535:40555,40557:40584,40594,40597:40600,40602,40604:40634,40636:40649 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 33411:33446,33505:33510 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 31404:31503 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 24375:24474 Failed: Going offline
13:58:13.730 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 17982:18081 Failed: Going offline
13:58:13.731 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 15302:15401 Failed: Going offline
13:58:13.731 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 12618:12717 Failed: Going offline
13:58:13.731 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 7586:7685 Failed: Going offline
13:58:13.731 Imap::Mailbox::FetchMsgMetadataTask [Gmail]/Important: UIDs 5554:5653 Failed: Going offline
13:58:13.731 conn Logged out.
13:58:13.740 *** Connection killed.