Incoming Email OK when sent from server using powershell cmd, but not from email client(outlook) from client machine - SharePoint

Hi,

I have successfully configured Central Admin settings/Exchange settings for Incoming email in SharePoint 2016. I am able to send email using below powershell commands from servers, where doclib@YYY.domainname.local is the email address for doclib.

Send-MailMessage -To doclib@YYY.domainname.local -from XXX@RRR.domainname.local -Subject "UAT Testing" -SmtpServer "SMTPSERVERNAME"

However , if I send email from my client machine outlook to the above address , it doesn't get stored in document library. I am suspecting if there is any blockage from firewall or its due to relay settings on SMTP server. Any inputs would be helpful a lot. Looking forward to hear from you. Thanks.