That's something folk tend to not get into. Since it wasn't secure in the first place, you have a bigger issue to tackle.

Now when we do have a secure email system, what happens? Please read https://en.wikipedia.org/wiki/Lavabit

Now if you didn't mean "secure" but had a leaked password, you may want to consider changing it on all your devices and stop storing it on all devices. Painful but it may be required.