We double check incoming vinyl supply, visually to make sure that there are no damages/dings/bended sleeves/seam splits etc. before it get listed. We use corrugated "frustration-free" four lax cardboard vinyl mailers in which we ship up to 5 x 10" and 12" vinyl formats reinforced with cardboard stiffeners. The corners are well protected because they have a corner crumple zone:

Four Lax vinyl mailer
For larger orders or box sets we use 3.5 mm up to 5 mm thick cardboard boxes reinforced with cardboard/thick paper/bubble wrap etc.
7" vinyl records up to 3 copies will be shipped in a 7" envelope mailer reinforced with 7" cardboard stiffeners:
Single envelope vinyl mailer
7" vinyl records up to 4-5 copies will be shipped in a 7" mailer box reinforced with 7" cardboard stiffeners:
Single vinyl mailer box

Factory sealed items will be shipped as they are but per request we can remove the shrink wrap and ship the vinyl record(s) outside the sleeve to avoid possible seam splits. Vinyl that have been released in a resealable plastic bag, will be shipped outside the sleeve to avoid any damages/seam splits during transit.