I am having issue that Yahoo emails are not reaching recipients.

I am having issue that Yahoo emails are not reaching recipients. I am getting an error message but after 24hrs not even straight after. It's only come to my attention because in follow up calls, they are telling me that the emails never arrived..

Please advise me how to sort it out as is very important I can reach those yahoo recipients.

Your message couldn't be delivered. Despite repeated attempts to contact the recipient's email system it didn't respond.

Contact the recipient by some other means (by phone, for example) and ask them to tell their email admin that it appears that their email system isn't accepting connection requests from your email system. Give them the error details shown below. It's likely that the recipient's email admin is the only one who can fix this problem.

For more information and tips to fix this issue see this article: https://go.microsoft.com/fwlink/?LinkId=389361.