Email service that does graylisting/razor/spamfiltering/etc?

I have about 20 domains, and any email to any of these domains
(anyaddress@any_of_my_domains.com) forwards to a single mailbox.

I handle email for all these domains myself, but it's becoming a hassle:

 % dictionary attacks mean I often get the same spam repeatedly

 % I'm too scared to change my SMTP config (to setup graylisting for
 example) for fear of breaking something and losing email [not that
 99+% of isn't spam anyway...]

 % My SMTP server sometimes gets flooded w/ connections (probably not
 denial-of-service-- just excess-of-spammers), delaying legit email.

In short, I want to to give up: running a mail server used to be easy,
but it's not anymore.

Is there a reliable, fairly inexpensive service that does graylisting,
razor-checking, sender address verification, RBL-checking, and other
spam filtering? Specifics:

 % I'd like to set the MX records for all 20 domains to their server
 and be done with it.

 % I do NOT want to forward email (to a spamarrest.com address for
 example). Forwarding means I still have to run my own mailserver +
 nullifies RBL checks, graylisting, etc.

 % I'd like the option of having challenge-response ("you sent me an
 email + I don't know you -- go here and prove you're human"), but
 also the option of turning it off.

 % Senders should always be notified (ideally at the SMTP level) if
 their message is rejected (ideally w/ a custom reject message that I
 choose). Messages shouldn't just disappear.

 % I'd like the ability to check my email via POP/IMAP. Size limits
 are OK: I plan to download email regularly.

 % Most of the email for my domains will come to just me, but I'd like
 the option to forward a copy of emails to certain addresses/domains
 to others. Example: email to *@domain1.com comes to just me, but
 email to [email protected] (that makes it through the spam filter)
 comes to me and a copy gets forwarded to bob-Re5JQEeQqe9fmgfxC/sS/[email protected] This feature
 isn't critical: I can probably setup Pine rules/etc to do what I want
 if I have to.

Any recommendations?

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