thanks for your answer.
Why is it common for https-providers to offer both RSA and EC certificates,
but it is not common for IMAP or SMTP
providers to offer EC certificates? I mean, if EC offers less calculations
without sacrificing security, why nobody
makes use of this?
Probably because the TLS parts of MTAs get less attention than the TLS
part of web browsers and servers. Everyone uses the same handful of
underlying crypto libraries (opensssl, gnutle, a few others) so in the
MTA it's mostly just tweaking parameters to the library calls.
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