Send SMTP email using System Net Mail via Exchange Online Office 365

Question

We are testing the new Office 365 beta  and i have a mail account on the Exchange Online service  Now I m trying to connect a LOB application that can send smtp emails from my test account   However the Exchange 365 platform requires TLS encryption on port 587  and there is a  feature  of System Net Mail that does not permit Implicit SSL encryption    Has anyone managed to get C  sending mails via this platform   I have the following basic code that should send the mail - any advice would be appreciated   SmtpClient server   new SmtpClient  ServerAddress    server Port   587  server EnableSsl   true  server Credentials   new System Net NetworkCredential  username mydomain com    password    server Timeout   5000  server UseDefaultCredentials   false   MailMessage mail   new MailMessage    mail From   new MailAddress  recipent anyaddress    mail To Add  username mydomain com    mail Subject    test out message sending   mail Body    this is my message body   mail IsBodyHtml   true   server Send mail

User · Answer

Office 365 use two servers  smtp server and protect extended sever   First server is smtp office365 com  property Host of smtp client  and second server is STARTTLS smtp office365 com  property TargetName of smtp client   Another thing is must put Usedefaultcredential  false before set networkcredentials       client UseDefaultCredentials   False     client Credentials   New NetworkCredential  user domain com    Password       client Host    smtp office365 com      client EnableSsl   true     client TargetName    STARTTLS smtp office365 com      client Port   587      client Send mail

User · Answer

Have you seen this  Sending email using Smtp mail microsoftonline com  Setting the UseDefaultCredentials after setting the Credentials would be resetting your Credentials property

User · Answer

Fixed a few typos in the working code above   MailMessage msg   new MailMessage    msg To Add new MailAddress  someone somedomain com    SomeOne     msg From   new MailAddress  you yourdomain com    You    msg Subject    This is a Test Mail   msg Body    This is a test message using Exchange OnLine   msg IsBodyHtml   true   SmtpClient client   new SmtpClient    client UseDefaultCredentials   false  client Credentials   new System Net NetworkCredential  your user name    your password    client Port   587     You can use Port 25 if 587 is blocked  mine is   client Host    smtp office365 com   client DeliveryMethod   SmtpDeliveryMethod Network  client EnableSsl   true  try       client Send msg       lblText Text    Message Sent Succesfully     catch  Exception ex        lblText Text   ex ToString        I have two web applications using the above code and both work fine without any trouble

User · Answer

In year of 2020  these code seems to return exception as   System Net Mail SmtpStatusCode MustIssueStartTlsFirst or The SMTP server requires a secure connection or the client was not authenticated  The server response was  5 7 57 SMTP  Client was not authenticated to send anonymous mail during MAIL FROM  This code is working for me               using  SmtpClient client   new SmtpClient                                 Host    smtp office365 com                   Port   587                  UseDefaultCredentials   false     This require to be before setting Credentials property                 DeliveryMethod   SmtpDeliveryMethod Network                  Credentials   new NetworkCredential  alias fulldomain com    password       you must give a full email address for authentication                  TargetName    STARTTLS smtp office365 com      Set to avoid MustIssueStartTlsFirst exception                 EnableSsl   true    Set to avoid secure connection exception                                               MailMessage message   new MailMessage                                         From   new MailAddress  alias fulldomain com       sender must be a full email address                     Subject   subject                      IsBodyHtml   true                      Body     lt h1 gt Hello World lt  h1 gt                        BodyEncoding   System Text Encoding UTF8                      SubjectEncoding   System Text Encoding UTF8                                      var toAddresses   recipients Split                       foreach  var to in toAddresses                                        message To Add to Trim                                        try                                       client Send message                                     catch  Exception ex                                        Debug WriteLine ex Message

User · Answer

Finally  Works   Put smtpClient UseDefaultCredentials   false  after smtpClient Credentials   credentials  then problem resolved               SmtpClient smtpClient   new SmtpClient smtpServerName                                         System Net NetworkCredential credentials   new System Net NetworkCredential smtpUName  smtpUNamePwd                smtpClient Credentials   credentials              smtpClient UseDefaultCredentials   false    lt -- Set This Line After Credentials              smtpClient Send mailMsg               smtpClient   null              mailMsg Dispose

User · Answer

Quick answer  the FROM address must exactly match the account you are sending from  or you will get a error 5 7 1 Client does not have permissions to send as this sender     My guess is that prevents email spoofing with your Office 365 account  otherwise you might be able to send as sballmer microsoft com   Another thing to try is in the authentication  fill in the third field with the domain  like  Dim smtpAuth   New System Net NetworkCredential       TheDude    hunter2password    MicrosoftOffice365Domain com     If that doesn t work  double check that you can log into the account at    https   portal microsoftonline com   Yet another thing to note is your Antivirus solution may be blocking programmatic access to ports 25 and 587 as a anti-spamming solution   Norton and McAfee may silently block access to these ports   Only enabling Mail and Socket debugging will allow you to notice it  see below    One last thing to note  the Send method is Asynchronous   If you call Dispose immediately after you call send  your are more than likely closing your connection before the mail is sent   Have your smtpClient instance listen for the OnSendCompleted event  and call dispose from there   You must use SendAsync method instead  the Send method does not raise this event     Detailed Answer  With Visual Studio  VB NET or C  doesn t matter   I made a simple form with a button that created the Mail Message  similar to that above   Then I added this to the application exe config  in the bin debug directory of my project    This enables the Output tab to have detailed debug info     lt  xml version  1 0  encoding  utf-8    gt   lt configuration gt       lt system diagnostics gt           lt sources gt               lt source name  System Net  gt                   lt listeners gt                       lt add name  System Net    gt                   lt  listeners gt               lt  source gt               lt source name  System Net Sockets  gt                   lt listeners gt                       lt add name  System Net    gt                   lt  listeners gt               lt  source gt           lt  sources gt           lt switches gt               lt add name  System Net  value  Verbose    gt               lt add name  System Net Sockets  value  Verbose    gt           lt  switches gt           lt sharedListeners gt               lt add name  System Net                type  System Diagnostics TextWriterTraceListener                initializeData  System Net log                gt           lt  sharedListeners gt           lt trace autoflush  true    gt       lt  system diagnostics gt   lt  configuration gt

User · Answer

Here is a side note for some that may be searching this thread for an answer to this problem   Be sure to read cautions at the bottom before implementing this solution   I was having trouble sending emails for a client to which my MS Office 365 subscription did not have a user or domain for  I was trying to SMTP through my Me MyDomain com 365 account but the  NET mail message was addressed from Client ClientDomain com  This is when the  5 7 1 Client does not have permissions  error popped up for me  To remedy  the MailMessage class needed to have the Sender property set to an email address that my supplied SMTP credentials had permission in O365 to  Send As   I chose to use my main account email  Me MyDomain com  as seen in the code below  Keep in mind I could have used ANY email address my O365 account had permission to  send as   i e  Support MyDomain com  no-reply MyDomain com  etc    using System  using System Net Mail   namespace ConsoleApplication1      class Program            static void Main string   args                   using               MailMessage message   new MailMessage                              To     new MailAddress  Recipient1 Recipient1Domain com    Recipient 1                     Sender   new MailAddress  Me MyDomain com    Me                   From   new MailAddress  Client ClientDomain com    Client                   Subject   net Testing                 Body  Testing  net emailing                  IsBodyHtml true                                                  using                  SmtpClient smtp   new SmtpClient                                    Host    smtp office365 com                     Port   587                    Credentials   new System Net NetworkCredential  Me MyDomain com    Pa55w0rd                      EnableSsl   true                                                             try   smtp Send message                    catch  Exception excp                                     Console Write excp Message                     Console ReadKey                                                               Please note SmtpClient is only disposable and able to use the Using block in  NET Framework 4 Users of  NET Framework 2 through 3 5 should use SmtpClient as such     SmtpClient smtp   new SmtpClient      Host    smtp office365 com      Port   587     Credentials   new System Net NetworkCredential  Me MyDomain com    Pa55w0rd       EnableSsl   true    try   smtp Send message     catch  Exception excp       Console Write excp Message      Console ReadKey        The resulting email s header will look something like this   Authentication-Results  spf none  sender IP is        smtp mailfrom Me MyDomain com    Received  from MyPC  192 168 1 1  by      BLUPR13MB0036 namprd13 prod outlook com  10 161 123 150  with Microsoft SMTP      Server  TLS  id 15 1 318 9  Mon  9 Nov 2015 16 06 58  0000   MIME-Version  1 0   From  Client  lt Client ClientDomain com gt    Sender  Me  lt Me MyDomain com gt    To  Recipient 1  lt Recipient1 Recipient1Domain com gt      -- Be Cautious -- Be aware some mail clients may display the Sender address as a note  For example Outlook will display something along these lines in the Reading Pane s header       Me  lt Me MyDomain com gt  on behalf of Client  lt Client ClientDomain com gt    However  so long as the email client the recipient uses isn t total garbage  this shouldn t effect the Reply To address  Reply To should still use the From address  To cover all your bases  you can also utilize the MailMessage ReplyToList property to afford every opportunity to the client to use the correct reply address     Also  be aware that some email servers may flat out reject any emails that are Sent On Behalf of another company siting Domain Owner Policy Restrictions  Be sure to test thoroughly and look for any bounce backs  I can tell you that my personal Hotmail  mail live com  email account is one that will reject messages I send on behalf of a certain client of mine but others clients go through fine  Although I suspect that it has something to do with my client s domain TXT  spf1  records  I do not have an answer as to why it will reject emails sent on behalf of one domain versus another  Maybe someone who knows can shed some light on the subject

User · Answer

I ve ported c  code used to work against smtp google com 587 to work via office365 without success  Tried all combinations of Credential before after using Ssl and almost every recommendation made on the Internet - w o success  got 5 7 1      error    Finally got this line from somewhere as last resort  just before  Send message   smtpClient TargetName    STARTTLS smtp office365 com     Since then - every send   is big success

[c#] Send SMTP email using System.Net.Mail via Exchange Online (Office 365)

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