Thanls Joria, it has been fixed in a most unexpected way: omni plant seed by time traveling. I had forgotten that was possible also.Still, ordering through the mailbox still don't work and I have no clue which bug has caused this, also I don't have the solution.
You can buy one with Buydebug? How? I've never saw it.
When you go into buydebug, go to the section that has plants/veggies for spawners. I think it is the third tab in, but not positive. Then the plants are listed alphabetically so after you find lettuce, then money tree, you should find omni plant. I used this to place some fully grown fruits and veggies on my empty, remodeled lots and public gardens. These plants when put on an empty lot, never need tending but will keep producing fruits and veggies after harvesting. The down side is they are only "normal" quality. Once a sim moves into the house though, then the garden requires tending and can eventually become perfect plants. Once someone lives there, if you don't tend it the plants will die! How does it know?
For omni plant it really doesn't matter if it is "normal" quality as it will produce the highest quality item fed to it, so my normal omni plants easily produced perfect death fish. If you fertilize it though it seems to produce more of an item than if you don't fertilize it, and they really do need some time off to rest. Also, sometimes you have to "refeed" a plant to make it produce. "Refeeding" also produces more items but I think it wears the plant out faster.
@ Athena: I think you can feed it fruits and veggies but why would you want to? I've never tried so can't say definitely. I have only fed expensive books and death fish. I think I may just plant a bunch from buydebug and try feeding odd items just to see what WILL be accepted. It would be good to know.
