Problem:
VMWare vCenter VCSA sendmail stat=Deferred [aaa.bbb.ccc.ddd] No Route To Host | email alerts failing
Solution 1)
vCenter (6.5+) > Configuration > General > Edit > Mail >
Use DNS hostname rather than IP address
Solution 2)
https://kb.vmware.com/s/article/2148396
Please consider crypto tipping: