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Klippy - try pinging gmx.com, if it ain't there, try again tomorrow, and tomorrow, and ...
This has been happening in various locations since November last year. UnitedInternet.de and subsidiaries like gmx and sites hosted by 1&1 disappear from DNS's. If gmx is still down trying pinging zabkat.com - if its down too, then its the same problem.
Given it has been happening for 6 months
I suggest using an alternative mail service, like maybe your ISP's, then at least, you'll have some leverage.
That's the problem with free - its the advertiser who has the leverage rather than the customer. The advertising costs are socialised to the people who buy the advertised products. This is known as free-market capitalism or communism by stealth.
BR