On 3/10/2017 7:48 AM, Brian Kantor wrote:
I think I've fixed the delay problem by adding more IP addresses to the greylister 'whitelist', but I don't know of anything I can do about the delivery problem.
Hotmail is notorious for silently deleting mail. Had a similar problem many years ago when working with a database developer who was working on the company's electronic booking system. The system sent out confirmation emails when people booked onto a course. However, we were getting complaints about confirmations not being received. On further investigation, we discovered that ALL of the affected people had Hotmail addresses. Further testing showed that Hotmail was silently deleting the automated emails, but manually sent email (i.e. from a regular client) worked fine. Never worked out what Hotmail didn't like, but it was highly annoying that it arbitrarily deleted email. Hotmail didn't even place them in the spam folder, they were simply deleted.
Only surefire solution is for those affected to ditch their Hotmail accounts. Anything else will work fine.