Error sending email using CDO on port 587 (TLS)

Question

Is there any trick to sending mail with CDO on port 587 (the port that uses TLS security protocol)?

This is my C++ code:

CDO::IMessagePtr iMsg(__uuidof(CDO::Message));
CDO::IConfigurationPtr iConf = iMsg->GetConfiguration();
CDO::FieldsPtr iFields;
_bstr_t empty("");
iConf->Load(CDO::cdoIIS,empty);  // this string constant from import
iFields = iConf->Fields;

iFields->Item["https://schemas.microsoft.com/cdo/configuration/smtpserver"]->Value = _variant_t(szServer);
iFields->Item["https://schemas.microsoft.com/cdo/configuration/smtpserverport"]->Value    = _variant_t(587);
iFields->Item["https//schemas.microsoft.com/cdo/configuration/sendusing"]->Value           = 2;
iFields->Item["https//schemas.microsoft.com/cdo/configuration/smtpauthenticate"]->Value = _variant_t(1); // Basic
iFields->Item["https//schemas.microsoft.com/cdo/configuration/sendusername"]->Value    = _variant_t(szUser);
iFields->Item["https//schemas.microsoft.com/cdo/configuration/sendpassword"]->Value     = _variant_t(szPassword);

if(iUseSSLTLS == 2)
    iFields->Item["https//schemas.microsoft.com/cdo/configuration/sendtls"]->Value = _variant_t(true);
else
    iFields->Item["https//schemas.microsoft.com/cdo/configuration/smtpusessl"]->Value = _variant_t(true);

iFields->Update();
etc... etc...

If I use this code with smtp.gmail.com:

server: smtp.gmail.com,
port: 587,
sndtls = true,
account: my gmail account,
password:

I obtain the following response:

Code = 8004020e,
Code meaning = Impossibile modificare o eliminare un oggetto che è stato aggiunto utilizzando COM+ Admin SDK,
Source = (null),
Description = Indirizzo del mittente respinto dal server. Risposta del server: 530 5.7.0 Must issue a STARTTLS command first. y2sm3575389wme.12 - gsmtp,

(sorry ... part of the message is in Italian language, but take a look at the bold/italic one)

Obviously, if I configure Outlook 2010 using the same parameters, it works perfectly.

One more thing, if I use port 465 and SSL:

server: smtp.gmail.com,
port: 465,
smtpusessl= true,
account: my gmail account,
password:

the code works fine, but I need to configure 587 port and TLS.

I eventually tried smtpusessl and sendtls together, setting them true:

iFields->Item["https//schemas.microsoft.com/cdo/configuration/sendtls"]->Value = _variant_t(true);
iFields->Item["https//schemas.microsoft.com/cdo/configuration/smtpusessl"]->Value = _variant_t(true);

And I obtain the following error:

Code = 80040213
Code meaning = IDispatch error #19
Source = CDO.Message.1
Description = The transport failed to connect to the server.

Do you meen; iFields->Item[... /sendtls"]->Value = _variant_t(true); iFields->Item[... /smtpusessl"]->Value = _variant_t(true); togheter? — Paolo Branzaglia, Jul 10 '17 at 10:46
no, I tried smtpusessl and sendtls together, setting them true and I obtain the following error: Code = 80040213 Code meaning = IDispatch error #19 Source = CDO.Message.1 Description = The transport failed to connect to the server. — Paolo Branzaglia, Jul 10 '17 at 14:58
Does this answer your question? [Using CDO/SMTP/TLS in VB6 to send email smtp.office365.com mail server](https://stackoverflow.com/questions/37530037/using-cdo-smtp-tls-in-vb6-to-send-email-smtp-office365-com-mail-server) — David G, Jun 05 '21 at 11:19

Paolo Branzaglia · Answer 1 · 2019-09-18T09:59:03.840

After over 2 years, I found a solution, well ... not a solution, but now I know why it didn't work, e why it will never work. It seems there's a bug in CDO library: it can handle STARTTLS command on port 25, but it can't on port 587.

You can read more here: https://social.technet.microsoft.com/Forums/en-US/37d00342-e5e9-4c8d-975d-44362332d426/bug-in-cdomessage-smtpserverport-587-fails?forum=ITCG

As I've just written above, it's a bug and I think Microsoft will never correct it. The recommendation for the future is to abandon CDO and use "Power shell" or third-party components.

Error sending email using CDO on port 587 (TLS)

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