The City of Dublin Steam Packet Company was a shipping line established in 1823. It served cross-channel routes between Britain and Ireland for over a century. For 70 of those years it transported the mail. It was 'wound-up' by a select committee of the House of Lords in 1922 and finally liquidated in 1930.

Royal Mail Ship, usually seen in its abbreviated form RMS, is the ship prefix used for seagoing vessels that carry mail under contract to the British Royal Mail. The designation dates back to 1840. Any vessel designated as "RMS" has the right both to fly the pennant of the Royal Mail when sailing and to include the Royal Mail "crown" insignia with any identifying device and/or design for the ship.