Fedora has issued an advisory on June 19:
The issue is fixed upstream in 1.12.0.
Assigning to wally as both registered and actual maintainer.
Fixed upstream in 1.12.0
Added an upstream patch  to fix the issue. Please test mutt-1.11.4-1.1.mga7 from core/updates_testing.
Updated mutt packages fix security vulnerability:
Invalid format of RFC parameter passed to atoi() function in rfc2231.c could
lead to unexpected behavior (rhbz#1710397, bdo#929017).
MGA7-64 Plasma on Lenovo B50
No installation issues.
Found some info on the use of mutt at https://www.thegeekdiary.com/how-to-install-and-configure-mutt-in-centos-rhel/
Tried to use mutt to send an e-mail from my hotmail account to my gmail account, but got into trouble defining the smtp parameters
MS seems to do something strange for "direct mail"
Swapped around, sending from gmail to hotmail gets me a bt further but still I run into a problem I cannot solve right now:
$ echo "" | mutt -s "testmutt" -i body.txt email@example.com
Verbinding met smtp.gmail.com beëindigd (Connection closed)
SMTP-sessie is mislukt: leesfout (smptp session failed: read error)
Bericht kon niet verstuurd worden. (message could not be sent)
The file body.txt used in the command just contains one line of plain text.