Hi, We have been using wwIPstuff to send emails for many years but are now having a problem with certain recipients mail servers refusing our emails. Example rejection - 550 5.0.350 Remote server returned an error -> 554 Transaction failed;Reject due to policy restrictions.

We have upgraded our internal mail server to office365 and it looks like some mail servers don't like the date header that is being sent as it removes the + on the date timestamp.

I have tried using a custom header for Date and forced the correct datestamp with the +0000 but upon sending, it still sends without.

I have created a logfile when sending emails to get an idea of whats being sent and you can see that the Date header is missing the +

2026.02.12 16:21:56:918 - snd: Date: Thu, 12 Feb 2026 16:21:56 0000

Is there any way around this?

I am using West Wind SMTP 5.0

Thanks in advance for your help.

Jason