MxToolbox is site that provides online tools to check if email works properly on specific domain.
What it does
Site takes email’s domain (part after @) as input.
Then it allows to check:
- if there is proper MX record set for domain;
- if SMTP functions resolve and work properly;
- if server IP listed in blacklists.
Set of tools is very comprehensive and easy to use. Aside from server checks there are more nice extras like parser for email headers and even free monitoring service (hadn’t tried it yet, but might be nice addition to Sucuri monitor).
It may take some effort and googling how exactly email works to interpret results, but overall site is easy to use and can be very convenient.