Run a service wash
A service wash means spinning the machine without any clothes in at a high temperature. Ideally done once a month, most manufacturers now recommend you use a certain cycle to do this or provide a special drum-cleaning program. Your instruction manual should have this information.
Clean the seal, drawer and filter
Mould and bacteria can fester in the rubber seal around the door hole. After washing have a look at the seal to see if it needs a scrub - doing this regularly can help prevent the build-up of mould and bacteria. If mould has had too long to fester, it may have sunk into the porous rubber of the seal and be impossible to remove.
If this happens it's most likely we need to replace the door seal.
Mould and bacteria also have a tendency to build up in the detergent drawer and lint filter. Leave the door and drawer open
Leaving the machine's door open after washing allows air to circulate in the drum and helps prevent the growth of mould and bacteria. You should also leave your machine's detergent drawer open for the same reason.
Check the stand pipe
If bad smells continue, there may be a partial blockage in the standpipe. If you suspect this is the case, use a drain unblocker to try and clear the pipe.