rasāñ : 'Causing to arrive, conveying, bearing; — one who conveys, bearer (used as last member of compounds)'. (Platts p.591)
tamkīñ : 'Gravity, dignity, majesty, grandeur, greatness, authority, power'. (Platts p.337)
sanj : 'Weighing, measuring; — weigher, measurer; examiner (used as last member of compounds)'. (Platts p.681)
tamkīñ-sanj = majestic/imposing. The Messenger, taking my letter, went to the beloved's place. She ought to have written a letter in reply, applied a seal to it, and given it to him. She didn't write a letter; on the Messenger's lips she applied a seal with sealing-wax/'lac' [lākh]. In this was a sign that in the future I should neither write anything and send it to her, nor send her any oral message. That was a very witty [ḳhvush-mażāq] beloved.
For more on Ghalib's unpublished verses, see the discussion in {4,8x}. See also the overview index.
On the nature and use of seals, see {61,5}. Perhaps the cruel beloved indeed used hot melted sealing-wax for her little pleasantry, as Gyan Chand maintains; if so, it's no wonder that the poor Messenger's lips were pallid or pale (I'm reading pīk as a variant of phīkā ), like the paper to which the seal ought properly to have been applied.
She sent the Messenger back with swollen or burnt lips-- it's almost like a warning from the Mafia! No doubt she wanted to enforce her 'dignity' or 'imposingness'. But as Gyan Chand also notes, she did find a very 'witty' way of replying to what was no doubt a long and tedious screed.
Note for grammar fans: To have the par before its clause, instead of after it, is archaic and Persianized ( like baġhair us ke instead of us ke baġhair ). It's almost never done with Indic postpositions. But whatever Ghalib wants, Ghalib gets.
Asi:
To my Messenger she didn't give a letter, but she pressed a seal on his lips. Through this gesture, the dignity-testing murderer sent, so to speak, a message of remaining silent.
== Asi, pp. 80-81