Sending emails through Classic ASP application -- 2

i have an online Classic ASP Application and emailing attached pdf files to the customers with using CDO.Message.
i am currently using my hosting SMTP server (most of emails are going to the Junk Email Folder and some emails don't deliver) but planning to use Microsoft Exchange SMTP server.

i need a very experience ASP / ASP.Net developer or a Microsoft Exchange Engineer for developing a new coding / Microsoft exchange server setup.
Maybe you can give me a better solution.

and second one;
i want to send the same emails as SMS message to the customer Mobile phone. I need this program. (we can use one of Free and Paid SMTP Services)

Please only very experience programmers.....


When it is not delivered, i receive this email
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
????????@???????.com
host gmail-smtp-in.l.google.com [2404:6800:4003:c01::1a]
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 [????????.com.au] did
550-5.7.26 not pass with ip: [2401:fc00:2:13f::6]. 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. t10-20020a170902e84a00b0019a826d3054si19597921plg.640 - gsmtp
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

My ASP Code
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
Set objMail = Server.CreateObject("CDO.Message")
Set objConf = Server.CreateObject("CDO.Configuration")
Set objFields = objConf.Fields
With objFields
.Item("http://schemas.microsoft.com/cdo/configuration/smtpserver") = "mail.????????.net.au"
.Item("http://schemas.microsoft.com/cdo/configuration/smtpserverport") = 587
.Item("http://schemas.microsoft.com/cdo/configuration/sendusing") = 2
.Item("http://schemas.microsoft.com/cdo/configuration/smtpconnectiontimeout") = 60
.Item("http://schemas.microsoft.com/cdo/configuration/smtpserverpickupdirectory") = "c:\inetpub\mailroot\pickup"
.Item("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate") = 1
.Item("http://schemas.microsoft.com/cdo/configuration/sendusername") = "pdf@????????.net.au"
.Item("http://schemas.microsoft.com/cdo/configuration/sendpassword") = "????????"
.Update
End With

With objMail
Set .Configuration = objConf
.From = strFrom
.To = strTo
.Subject = strSubject
if attachFileNameExist = "yes" then
.AddAttachment strPathTerms&"\images\termsPDF\"&attachFileName
end if
.HTMLBody = Replace(strBody, chr(13), "<br>")
End With

Err.Clear
on error resume next

objMail.Send
Set objFields = Nothing
Set objConf = Nothing
Set objMail = Nothing
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""