Just loaded a large number of users using the windows power shell.
Set-MailEnableMailbox -Postoffice xxx.com -Mailbox yyy -Setting mailboxLimit -Value 528000
These users are not able to send emails to each other, while some can and some cant, they can however send email out but they are not receiving emails at all. Error: Reason: Remote SMTP Server Returned: 503
Checked and followed the instructions on https://www.mailenable.com/kb/content/article.asp?ID=ME020531
Any advice?