Hello,
From my customer not send mail to @viseo.com and @pacplast.pl(I know only these now).
I search both MXrecords "Viseo-com.mail.protection.outlook.com"and "pacplast-pl.mail.eo.outlook.com"(Both have Office365)
IP Address for both records is 213.199.154.23 and 213.199.154.87.
In me the answer PING for both is 213.199.154.87 => sending mail works.
In customer the answer PING for both is213.199.154.23 => sending mail does not work.
Both use the same DNS (8.8.8.8and 8.8.4.4, I also triedother). I try flushdns and ClearCache in DNS server.
If I set HOST A record for "Viseo-com.mail.protection.outlook.com" toaddress 213.199.154.87 in local DNS server, then sending mail works.
How solve this? I'm afraidit will do for alltargets with office365.