[exim] DKIM: validation error: LONG_LINE

Greetings,

A certain device within our organization is relaying email via our EXIM
systems but EXIM is unable to sign the message. The vast majority of our
other messages are signed without issues.

Here is the corresponding error from the log.

2021-04-21 14:34:48 1lZDwB-0003pb-TY DKIM: validation error: LONG_LINE
2021-04-21 14:34:48 1lZDwB-0003pb-TY DKIM: Error during validation, disabling signature verification: LONG_LINE
2021-04-21 14:34:48 1lZDwB-0003pb-TY <= XXXXXXXXXX@XXXXXXXXXXX H=XXXXXXXXXXXXX (PowerXpert-00-20-85-FC-86-BE) [X.X.X.X] P=esmtp K S=1684783 id=0_0d_-1_1032
2021-04-21 14:34:49 1lZDwB-0003pb-TY DKIM: signing failed: LONG_LINE
2021-04-21 14:34:50 1lZDwB-0003pb-TY => XXXXXXXXXXX@XXXXXXXXXXX R=dnslookup T=remote_smtp S=1703743 H=XXXXXXXXXXX.mail.protection.outlook.com [104.47.61.36]:25 X=TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256 CV=yes K C="250 2.6.0 <0_0d_-1_1032> [InternalId=23656679878773, Hostname=DM6PR12MB4747.namprd12.prod.outlook.com] 1711342 bytes in 0.383, 4354.433 KB/sec Queued mail for delivery" DT=1s
2021-04-21 14:34:50 1lZDwB-0003pb-TY Completed

The DKIM LONG_LINE errors are also output to the paniclog.

EXIM version = 4.92.3

Regards,
Wayne