Unable to send message. Check sender, recipients and message body error

[Luvic95]

Hello, I've using this app for about 2 years now but have recently been getting this "Unable to send message. Check sender, recipients and message body" error message while using the wizard.

SMTP host: mail.smtp2go.com
SMTP port: 2525                                                                                                                                                             
Connecting to SMTP socket (mail.smtp2go.com:2525)...                                                                                                                        
Starting TLS session...
Disable authentication (Y/N)?: N
Username: *******                                                                                                                                          
Password:  *******                                                                                                                                                                                                                                                                                                                             
Authentication successful                                                                                                                                                   
Sender address: test@test.com
Sender name: TEst                                                                                                                                                           
Recipient address: myemail@gmail.com                                                                                                                                
Enter additional recipients (Y/N)?: N                                                                                                                                       
Subject line: TEst                                                                                                                                                          
Load message body from file (Y/N)?: Y                                                                                                                                       
Filename: example.html                                                                                                                                                      
Send message (Y/N)?: Y                                                                                                                                                      
Sending spoofed message...                                                                                                                                                  
Unable to send message. Check sender, recipients and message body

Get the same error when loading email content directly too.
Does your app still work with smtp2go ?

[mikechabot]

And you've been entering the same values into the wizard? In that case, it's possible smtp2go restricted access for your user. Try logging in to confirm you haven't hit any limits in place, or try creating another account, otherwise you may want to find an alternative to smtp2go. You'd just want to look for free smtp servers.

[mikechabot]

Definitely an issue stemming from sendmail. I can update it to log the exact error, but let me know if any of the above works.

smtp-email-spoofer-py/spoofer/models/smtpconnection.py

Line 98 in 7632281

except smtplib.SMTPException:

[bogaco]

Hi @mikechabot,

Unfortunately, creating another smtp2go account didn't work for me and I am getting the same error that @Luvic95 has got. Would appreciate it if you could update sendmail.

[Luvic95]

@bogaco Yeahh.. Creating another account didnt work for me either. I believe its because Smtp2go has added domain validation now. I think that is the source of the problem (I might be wrong. idk), I am still trying to find a smtp service provider that does not do this validation. I will update you as soon as I manage to find a solution on my end too.

[mikechabot]

So here's the full stack trace; basically it boils down to unable to verify sender address. Looks like smtp2go has implemented some protective measures to thwart this type of spoofing. I spoofed the sender as john@example.com.

Send message (Y/N)?: y
Sending spoofed message...
Unable to send message. Check sender, recipients and message body

Traceback (most recent call last):
  File "C:\_workspaces\smtp-email-spoofer-py\spoofer\models\smtpconnection.py", line 97, in send_mail
    self.server.sendmail(self.sender, self.recipients, message.as_string())
  File "C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python37_64\lib\smtplib.py", line 881, in sendmail
    raise SMTPRecipientsRefused(senderrs)
smtplib.SMTPRecipientsRefused: {'mypersonalemail@live.com': (550, b'unable to verify sender address.')}

Here's their bit of info: https://support.smtp2go.com/hc/en-gb/articles/223087847--Unable-To-Verify-Sender-Address-Error-Message

Going to try with a valid email address as the sender that I own.

[mikechabot]

Okay, so when sending from a valid email address, where the domain has a proper MX record, it seems to work.

Now if you own the sending address, which I do above, it essentially defeats the purpose of spoofing, since you'd just use that particular mail client. However, it seems you would be able to spoof mail from any known email address that you don't own. I cannot endorse or condone that behavior, but it does appear possible.

[mikechabot]

Closing this out; smtp2go now ensures that a valid MX record exists for the spoofed message sender. One option is to try to locate another open SMTP provider; otherwise you'd need to spoof a valid email address, which I cannot condone or advise, unless you own it.