Man pages matching name mail::message::transferenc::base64 in section 3pm:

Mail::Message::TransferEnc::Base64.3pm.en	debian 10 / libmail-message-perl
Mail::Message::TransferEnc::Base64.3pm.en	debian 11 / libmail-message-perl
Mail::Message::TransferEnc::Base64.3pm.en	debian 12 / libmail-message-perl