A lot of different tools are around the internet which can be useful to determine different SMTP troubles.
The most of them are very useful but they are all reachable over the internet and don’t provide any kind of API for integration of monitoring or complex integration in (pre)deployment pipelines.
This is a short overview of some command line tools for developers and administrators, to check the e-mail flow during developing, emulate and intercept outgoing emails and afterwards for maintaining the setups.
