Actually, thinking about it I changed my mind :-) I think it should be considered a bug, mail-notification should suggest instead of recommend mail-notification-evolution ("The Recommends field should list packages that would be found together with this one in all but unusual installations" -- using Thunderbird instead of Evolution seems to be not that uncommon). There's already a Debian bug for this issue. Please add any further comments to that bug.
Actually, thinking about it I changed my mind :-) I think it should be considered a bug, mail-notification should suggest instead of recommend mail-notificati on-evolution ("The Recommends field should list packages that would be found together with this one in all but unusual installations" -- using Thunderbird instead of Evolution seems to be not that uncommon). There's already a Debian bug for this issue. Please add any further comments to that bug.