The cover is valued at £35,000-40,000 ($54,163-61,900), bearing "1 Anna" hand stamped in dull violet on a 4 anna brown horizontal strip of three.
The cover is the only recorded multiple of the hand stamped provisionals, and one of only two covers recorded bearing this particular provisional. It is also the earliest recorded usage of the stamp, making it one of the most important of all provisional covers.
Another Mombasa cover is expected to bring the second highest bids at £28,000-30,000 ($43,330-46,495).
The cover is unusual in that it bears Indian stamps, which would have been obtained from Zanzibar and used in the British East Africa Co. Post Office following the purchase of the Mombasa stock from the first issue by Whitfield King & Co.
The 1890 Easter Telegraph Company Limited printed envelope features a ½ anna blue-green, 1 anna plum, 2 anna blue, 8 anna dull mauve and 1 rupee slate, resulting in a total of 51½ annas, which would pay 11 times the 4½ anna rate to the UK.
Starring among the single stamps on offer is an 1895 "1 anna" on 3 anna provisional, which has been initialled "TECR" by the Mombasa postmaster TEC Remington.
Boasting brilliant colour, with nearly full original gum, it is the finest example of the rare stamp known, of which there are just four unused examples. It is expected to sell for £17,000-20,000 ($26,307-30,950).