[dev] OTRS: using SHA-256 algorithm for IMAPS sessions

Hi. We are using OTRS, which receive mail through external mail provider via IMAPS. Mail provider is going to stop supporting mail clients which use unsafe SHA-1 signing algorithm. To continue using this mail provider we must be sure that our OTRS uses exactly SHA-256 algorithm to sign certificates during IMAPS session. How could I check, what signing algorithm is used for IMAPS? Where can i find configs for this? OTRS: 4.0.13 OS: CentOS 7.1