Using the mail function, we cannot send emails via DMX. Emails work on the entire site except DMX. We get the following error:

AssemblyVersion:7.3.4
PortalID:0
UserID:3224
ActiveTabID:2795
ActiveTabName:Downloads
RawURL:/ServiceSupport/Downloads.aspx?EntryId=399
AbsoluteURL:/Default.aspx
UserAgent:Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.112 Safari/537.36
DefaultDataProvider:DotNetNuke.Data.SqlDataProvider, DotNetNuke
ExceptionGUID:4c3e60fc-eda1-40c7-9eb1-0d902b62af43
InnerException:Failure sending mail.
FileName:
FileLineNumber:0
FileColumnNumber:0
Method:System.Net.Mail.SmtpReplyReaderFactory.ProcessRead
StackTrace:
Message:
System.Net.Mail.SmtpException: Failure sending mail. ---> System.IO.IOException: Unable to read data from the transport connection: net_io_connectionclosed.
at System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte[] buffer, Int32 offset, Int32 read, Boolean readLine)
at System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine)
at System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller)
at System.Net.Mail.CheckCommand.Send(SmtpConnection conn, String& response)
at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode)
at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception)
at System.Net.Mail.SmtpClient.Send(MailMessage message)
--- End of inner exception stack trace ---
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at Bring2mind.DNN.Modules.DMX.Services.Notification.NotificationController.SendMail(Int32 PortalId, MailMessage message)

DMX version 6.1.6

Please advise...

What settings are you using for SMTP for the site?

DMX Version: 6.1.6
DNN Version: 7.3.4
SMTP Settings:
Server/Port: smtp.sendgrid.net:587
Connection Limit: 10
Max Idle Time: 0
SMTP Authentication: Basic
SMTP Enable SMTP (non checked)
SMTP Username:
SMTP Password:

SMTP works everywhere on site but the document manager.

There was a fix in 6.1.7 regarding SMTP and SSL.

This resolved our issue. Thank you.