During an address list folding when a separating comma ends up on a folded line and that line is to be unicode-encoded then the separator itself is also unicode-encoded. Expected behavior is that the separating comma remains a plan comma. This can result in the address header being misinterpreted by some mail servers.
Exploitability
AV:NAC:HAT:PPR:LUI:NVulnerable System
VC:LVI:NVA:NSubsequent System
SC:NSI:NSA:N2.3/CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N