Help WHMCS didn't send email to yahoo email address

[host]

Whmcs is not sending email to yahoo customer. because i only get complains from those customer who have a yahoo email address. Please tell me how i resolve this problem?
Thanks in advance

[libertyreservehosting]

Thats probably you haven't configured your SMTP
Maybe you are using PHP mail as your mail setting. Change it to SMTP and the problem might get resolved

Hope this helps

[host]

Thanks madihib i check the mail ip address http://www.mxtoolbox.com/blacklists.aspx and find out mail server ip of customer is blacklist that why mail didn't delivered