Exim - retry time not reached for any host

[Mike Clarke]

I'm running exim-sa-exim-4.94+4.2.1 on FreeBSD 12.1-RELEASE-p5.
I've been using exim for several years without much trouble apart from the occasional 'retry time 
not reached for any host' error. I can normally clear these by running exim_tidydb and sometimes 
deleting files from /var/spool/exim/db.
However since yesterday I'm constantly getting these errors which I cannot clear. I've tried 
exim_tidydb, deleting files from /var/spool/exim/db and deleting all messages stuck in the queue 
but every time I try to send an outgoing email I get messages in the logfile like this:
2020-06-19 16:20:14 1jmIoQ-0008AM-5d <= REDACTED at REDACTED H=(curlew.localnet) 
[127.0.0.1] P=esmtp S=1539 id=1788122.tpkKSVv8f3 at curlew
2020-06-19 16:20:14 1jmIoQ-0008AM-5d == REDACTED at gmail.com R=sedbergh_route 
T=remote_auth_smtp defer (-37) H=sedbergh.org.uk [206.189.20.173]: TLS session: (SSL_connect): 
error:00000000:lib(0):func(0):reason(0)

Then every time the queue runner starts I get a 'retry time not reached' message

2020-06-19 16:23:01 Start queue run: pid=32029
2020-06-19 16:23:01 1jmIoQ-0008AM-5d == REDACTED at gmail.com R=sedbergh_route 
T=remote_auth_smtp defer (-53): retry time not reached for any host for 'gmail.com'
2020-06-19 16:23:01 End queue run: pid=32029

I've tried sending to various recipients with the same result.

I can use three different remote servers, operated by different service providers, and I get the same 
problem with each of them.

Although I have this problem with exim I can send directly to the same servers directly from kmail 
using the login credentials copied and pasted from my exim configuration files.

So it looks very much like the problem lies somewhere in my system even though there's been no 
changes made recently. I'd appreciate suggestions on how I should go about tracing and fixing the 
cause of this problem.

-- 
Mike Clarke