There were 3,364 bags of mail on the Titanic, which (it is often forgotten was registered as a mail ship - that's what the RMS stands for).

As some of the mail had been moved upstairs when the mailroom started to flood, there's a possibility it may be relatively accessible compared to items deep in the bow, and the remaining items may still be in-situ relatively undisturbed given that the bow flooded more gradually than the stern.

Pretty sure there was an ROV either in the post office or the storage room on one expedition that actually did see mailbags that looked pretty damn well preserved. I saw photos of them a few years ago but I can’t really find them anymore. They did have some kind of mold growing on them too. There was a discussion about removing them by cutting through Titanics hull but a court in Virginia denied them (rightfully so. Cutting the hull is definitely a step too far).