spf dkim

I keep getting this error message when ever I send any messages to Gmail users lately. Please help!

    SMTP error from remote mail server after end of data:

    550-5.7.26 This mail is unauthenticated, which poses a security risk to the

    550-5.7.26 sender and Gmail users, and has been blocked. The sender must

    550-5.7.26 authenticate with at least one of SPF or DKIM. For this message,

    550-5.7.26 DKIM checks did not pass and SPF check for [srustiarchitects.com]

    550-5.7.26 did not pass with ip: [66.96.186.8]. The sender should visit

    550-5.7.26  https://support.google.com/mail/answer/81126#authentication for

    550 5.7.26 instructions on setting up authentication. oy11-20020a170907104b00b0096f70603c8dsi442292ejb.30 -