E-mail problems since upgrading to new version

my website is (redacted)
Since upgrading to newest version, I am not getting confirmation of emails or when I try to change a status of orders, I get this error message.

2020-08-13 17:38:28 CLIENT -> SERVER: EHLO (redacted)
2020-08-13 17:38:28 CLIENT -> SERVER: STARTTLS
2020-08-13 17:38:28 CLIENT -> SERVER: EHLO (redacted)
2020-08-13 17:38:28 CLIENT -> SERVER: AUTH LOGIN
2020-08-13 17:38:28 CLIENT -> SERVER: [credentials hidden]
2020-08-13 17:38:28 CLIENT -> SERVER: [credentials hidden]
2020-08-13 17:38:28 SMTP ERROR: Password command failed: 535-5.7.8 Username and Password not accepted. Learn more at535 5.7.8 https://support.google.com/mail/?p=BadCredentials k31sm7129697qtd.60 - gsmtp
SMTP Error: Could not authenticate.
2020-08-13 17:38:28 CLIENT -> SERVER: QUIT
SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting
WARNING: An Error occurred, please refresh the page and try again.If you were entering information, press the BACK button in your browser and re-check the information you had entered to be sure you left no blank fields.

My "contact us" link doesn't come up on my website unless you are logged in and even then still doesn't work.

Does anyone know what to do to correct these issues?

Look in Admin > Configuration > E-Mail Options and go to the bottom and check your SMTP credentials (especially the password). Perhaps they changed?

To use email (eg SMTPAUTH) with a Google mail account you need to enable "allow less secure authentication" inside your google account settings.
This isn't "new", and isn't specific to any Zen Cart version. But maybe you recently changed your security levels in your google mail account?

swguy:

Look in Admin > Configuration > E-Mail Options and go to the bottom and check your SMTP credentials (especially the password). Perhaps they changed?
... and make sure that your password doesn't include any HTML special characters, i.e. "><&.

I can't find where to change that. I looked under all my gmail settings.

SCOX5275:

I can't find where to change that. I looked under all my gmail settings.
On this page they explain how to "turn on the Less Secure Apps" setting (they also recommend turning it off, but the way Zen Cart sends email requires the "less secure apps" method. (Ya, the wording of "less secure" sounds foreboding, but it's still secure.))
And, yes, "gmail transport" or "SMTPAUTH" are fine.
https://support.google.com/accounts/answer/6010255?hl=en

Trying to get 1.5.7a to work with GMAIL for sending emails.
Zen Cart 1.5.7

Database Patch Level: 1.5.7
PHP v 7.3.21 (Zend: 3.3.21)

I have verified password is entered correctly

SMTP Email Account Mailbox (redacted)
SMTP Email Account Password ****************
SMTP Email Mail Host smtp.gmail.com
SMTP Email Mail Server Port 587

His account is using 2FA, I have created a 3rd party app MAIL and was given a 16 character password
I have installed the run the DB file to incorporate GMAIL as a Transport method and have tried the following combination of sending methods

• smtpauth with each of smtp.gmail.com and relay-smtp.gmail.com, 587 and 465
• smtp same as above
• Gmail same as above

With all of them, I get the following error: PHP Notice: Email Error: SMTP connect() failed.

Looking for some insight

While various points are already mentioned in this thread, several additional points are covered in the docs:
https://docs.zen-cart.com/user/email/external_smtp_servers/#google-mail--gmail

because its 2 factor authentication, and because he has his suite account thru his host, its the main culprit. I created a work around by creating a a mail forwarder, using the the phpwrapper and forwarding emails to his gmail account. is working that way. I believe the issue he was having is related to his domain/host and not the cart.