Mail stuck in queue - connection refused?

Question

I've just looked at the mail spool and was alarmed to see 18 mails stuck in there with subjects like "test email", "test" etc from clients within our network going to important external clients. Obviously our internal users know there is something wrong with delivery hence the titles of the mail. 
 For this particular domain they are sending to, I'm getting: 
 2016-04-25 15:16:08 XXXXX@XXXXX.uk R=dnslookup T=remote_smtp defer (-53): retry time not reached for any host 
 2016-04-25 18:02:45 mail.YYYYY.uk [150.70.226.147]:25 Connection refused 
 2016-04-25 18:02:45 XXXXXX@XXXXXX.uk R=dnslookup T=remote_smtp defer (111): Connection refused 
 2016-04-25 18:08:27 mail.YYYYYY.uk [150.70.226.147]:25 Connection refused 
 2016-04-25 18:08:27 XXXXXXX@XXXXXX.uk R=dnslookup T=remote_smtp defer (111): Connection refused 
 2016-04-25 18:21:16 mail.YYYYY.uk [150.70.226.147]:25 Connection refused So, it's resolving the mail server and for some reason looks to get refused. I'm not on any blacklists and checking the mxrecords etc, we are set up fine. 99% of other mail is getting delivered (both in and out) I do however, have a couple of other domains that behave like this.

Louis-M · Accepted Answer

ummmmmhhhh 
 Finally solved. It seems i had set some country blocking on the firewall. 
 And although I was sending to only .uk addresses, their cloud mail servers were in various places that I'd blocked at the firewall. 
 Turning Country blocking off resolved this. One to look out for in the future.