smtp.mppmu.mpg.de has no MX records.
Question and response
Question
dig smtp.mppmu.mpg.de. MX
Answer
The response has no answer records.
Authority
mppmu.mpg.de. 600 SOA iws132a.mppmu.mpg.de. uwl.mppmu.mpg.de. 2026021400 10800 1800 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0