Sending email using CDO from VB6 app is slow

I have a simple VB6 app that uses CDO to send email.  It's worked perfectly for the past 2 years.  A few days ago, it began having  speed issues.  Rather than sending multiple emails in less than a second, it now takes 5-10 seconds to send a single email.  The code hangs on the .Send command.
To my knowledge, there have been no changes made to our network over the past week.  I've checked patch logs, asked if anyone made any Group Policy changes, software installs - nothing changed recently.  
The .send command works, but way too slow.
Any ideas here?

Dim Cdo2Configuration As cdo.Configuration
    Dim Cdo2Message As cdo.Message
    Dim Cdo2Fields As ADODB.Fields
    
    Set Cdo2Configuration = New cdo.Configuration
    Set Cdo2Fields = Cdo2Configuration.Fields
    With Cdo2Fields
      .Item(cdoSMTPServer) = "Exchange_Server_Name"
      .Item(cdoSendUsingMethod) = cdoSendUsingPort
      .Item(cdoSMTPConnectionTimeout) = 15
      .Update ' Important
    End With
    
    ' Create a new message.
    Set Cdo2Message = New cdo.Message
    
    ' Set the message's configuration.
    Set Cdo2Message.Configuration = Cdo2Configuration
    
    ' Set the message content.
    Cdo2Message.Subject = sSubject
    Cdo2Message.TextBody = sBody
    Cdo2Message.HTMLBody = sHtmlBody
    
    ' Address the message.
    Cdo2Message.Sender = sSender
    Cdo2Message.From = sSender
    Cdo2Message.To = sTo
 
    ' Send the message.
    Cdo2Message.Send
    
    Set Cdo2Message = Nothing
    Set Cdo2Configuration = Nothing
    Set Cdo2Fields = Nothing

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