Why can't I send a digital quotation, sales invoice or reminder by email?

Disclaimer

All screenshots in the article were taken in the Dutch version of Yuki.

There are a number of reasons why Yuki cannot send a digital quote, sales invoice or reminder by email to the customer:

• Sending method is not set correctly in quotation, invoice or reminder to be sent
  Field 'Sending method' should be: 'Send by email'.
  
  
  
• Sending method is not set correctly in Yuki in the Sales Settings in the domain
  Sending method should be: 'All by email' or ‘Where possible by email’.
  
  
  
• Email account in Yuki from which to send email (sender email address) is not yet verified
  Confirm email account from the mailbox of the email account in question.
  
  
  After confirming this email, the status of your email account in Yuki will change to ‘Active’.
  
  
  
• Sending through own SMTP server (outgoing mail server): 
  • Login credentials (username and password) that allow access to own SMTP server (which handles e-mail) are not correct
    When this is the case, the following error message may appear: "Error sending e-mail through the specified SMTP server ... with username ... Check your username and/or password.535 5.7.8 Error: authentication failed: authentication failure ]".
    
    
  • Two-factor authentication is used on own SMTP server (which handles email)
    This is not supported from Yuki when sending email.
    When this is the case, the following error message may appear: "Error sending email through the specified SMTP server ... with username ... Check your username and/or password.535 5.7.8 Error: authentication failed: authentication failure ]".
    
    In this case, an app password must be entered to allow access to your own Microsoft account, Google account or Office 365 account on your own SMTP mail server.
    
    For more information on creating and using an app password:
    • with a Microsoft account see Using app passwords with apps that do not support two-step authentication
    • with your Google account see Logging in with app passwords