Email Deliverability Issue

I'm up against an odd one this morning, some of my users on outlook are not getting emails although they're hitting their server and they're viewable when viewed via Roundcube. I've had a look at the logs and I see the following, but cant spot anything untoward. 2020-03-20 11:27:34 SMTP connection from [217.34.244.***]:61711 (TCP/IP connection count = 4) 2020-03-20 11:27:34 1jFFoM-0001jz-IP H=host217-34-244-***.in-addr.example.com ([192.168.0.30]) [217.34.244.***]:61711 Warning: Message has been scanned: no virus or other harmful content was found 2020-03-20 11:27:34 1jFFoM-0001jz-IP <= lee.logan@domain.com H=host217-34-244-***.in-addr.example.com ([192.168.0.**]) [217.34.244.***]:61711 P=esmtpsa X=TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256 CV=no A=dovecot_plain:lee@domain.com S=55156 id=E74D10BD-9F4E-435C-BBCD-D6948E23A59C@domain.com T="test" for alison@domain.com 2020-03-20 11:27:34 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc 1jFFoM-0001jz-IP 2020-03-20 11:27:35 SMTP connection from [46.38.145.***]:60237 lost D=14s 2020-03-20 11:27:35 1jFFoM-0001jz-IP => alison R=virtual_user T=dovecot_virtual_delivery C="250 2.0.0 CHx2AKeodF7RGQAA6nrpTQ Saved" 2020-03-20 11:27:35 1jFFoM-0001jz-IP Completed [root@domain ~]#
Can anyone offer any advice, Thanks in advance. Lee