Softhome.net is one of the most longstanding and free (they also have a paid version) email servers that have proven to be reliable over a long period of time.
Offering an email service that can be accessed via either pop3 (for example webmail) or a webclient, Softhome say that they use greylisting as a way to stop spam and viruses by operating in such a way as to ensure that both fail due to the way they were designed.
One less positive side of this is that email can sometimes comes through slowly, this is the greylisting process in effect – it is protecting your mailbox.
If mail has previously been successfully delivered from a specific email address then this is likely to come through much fast because it has already been cleared, according to Softhome.
Professional (paid) users of the service have the option to turn this on or off as well as Softhome operating both blacklists and whitelists.