Email could no be sent

Gmail?

yes gmail

You need to use OAuth 2.0
https://googleonlinesecurity.blogspot.ca/2014/04/new-security-measures-will-affect-older.html

this is a new rule?

Google started rolling out the new rules in the summer of 2014.

is it difficult to use OAuth 2.0 ???

I’m afraid I don’t know how to use OAuth 2.0 for my wp site ??

Do you mean I must ask my host to switch my account to OAuth 2.0 ?

This is between you and Google, not your host.

oh thank you very-much

you mean if I use now this protocol
wp mail smpt will work fine again ?

i can use Postman SMTP Mailer plugin with wp mail smpt both on my wp site ?

No. Wp Mail SMTP does not support OAuth 2.0. It only supports the older authentication.

Oh yes
so it’s better for me to delete wp mail smpt

and now try to use this new Postman SMTP Mailer plugin

to get my email sent by my wp site ?

Try it and make sure before you delete anything. Another option is to use WP Mail SMTP with something else besides Gmail.

oh yes with yahoo for example ?