It's not the connection, it's the size of the post. Up size to a 6x6 next go around. I'd add that footing too.

al

Sounds like the rim joist may be rolling over. How you fix it depends on the surrounding structure. How far off the ground is the deck? If you're up off the ground a bit, you could extend the post down below the rim joist, then add a support under the deck that prevents the bottom of the post from leaning in (and thus the top from leaning out). The post length below the rim joist will need to be at least 2/3 the length above for this to work. If your deck is closer to the ground, then you can set this post directly into the footing, so long as the footing is deep enough (30" or so ought to do it).

Be aware that if you make the structure more rigid using one of these options, the post itself may bow over time due to the weight (rather than simply leaning as it's doing now). In that case, a bigger post may be required, but you'll still need to stiffen up the structure.