Fixing mail delivery issue

We have an issue with our mail server, when we send email to gmail users we receive Mail delivery failed: returning message to sender host [login to view URL] [[login to view URL]] SMTP error from remote mail server after pipelined end of data: 550-5.7.1 [[login to view URL] 19] Our system has detected that this message is 550-5.7.1 likely suspicious due to the very low reputation of the sending 550-5.7.1 domain. To best protect our users from spam, the message has been And we tried to send to another mail server 2021-11-08 20:52:41 1mk8on-0006Nv-Vn [[login to view URL]] SSL verify error: certificate name mismatch: DN="/C=US/ST=California/L=San Jose/O=Cisco Systems/CN=Cisco ESA Certificate" H="[login to view URL]" 2021-11-08 20:52:41 1mk8on-0006Nv-Vn failed to expand dkim_domain: unknown lookup type "lsearch,ret=key" Hotmail is receiving email, but in junk We need a freelancer to fix the mail delivery issue using a TeamViewer access.