It is safe enough to reject mail during the envelope phase. If it is spam, the sender will just discard it and may even blacklist you so as to not waste more time. If it is a valid sender, they can resend. In my case, I run no spam filter, I only drop messages sent to bogus accounts. If someone misspells my account, they can correct it easily enough, if they care.
Even if your spam filter mistakenly rejects a message during the envelope phase, a legitimate sender can obfuscate the buzzwords if they care enough. If it is a bank or such, they shouldn't be sending likely spam words anyway.