After 2019.03.23 we cannot send or receive any emails. But it is possible to send mail to gmail addresses.

following is the error message shown, when trying to resend. 

4.7.500 Server busy. Please try again later from [136.143.188.53]. (AS77713295) [PU1APC01FT046.eop-APC01.prod.protection.outlook.com]

Thanks! ​