Do you trust the person on the receiving side? Presumably so if you are sending them something, but once it leaves your computer its out of your control. The recipient could do something like accidentally (or intentionally) forward or reply in the clear, or could have malware on their computer that copies emails as soon as they are decrypted.
Comments
What are you protecting, and who are you protecting it against?
I knew that well funded government agencies could probably get access to anything, so with that caveat yes, I trusted a few providers.
In general if it's important you shouldn't trust anyone. Use GPG, but do so carefully after reading all the documentation.
Do you trust the person on the receiving side? Presumably so if you are sending them something, but once it leaves your computer its out of your control. The recipient could do something like accidentally (or intentionally) forward or reply in the clear, or could have malware on their computer that copies emails as soon as they are decrypted.