Does Mailgun have any throttling to send over SMTP?

Question

Mail server

Found that since March 23, smtp throws out an error that it is not possible to connect. The error occurs under load.
Today I tested with the send limit settings once per second. Errors continue to occur.

Very strange behaviour.
Already forgot how the SMTP protocol works. Whether it can fall off on the server side. Or exactly Mailgun.
Their tech support is still silent.

maybe it has something to do with the standard laravel mailer