Downloading http://mirror.yandex.ru/debian/dists/stretch/InRelease...
Downloading http://mirror.yandex.ru/debian/dists/stretch/Release...
Downloading http://mirror.yandex.ru/debian/dists/stretch/Release.gpg...
gpgv:  RSA key ID 46925553
gpgv: Good signature from "Debian Archive Automatic Signing Key (7.0/wheezy) <ftpmaster@debian.org>"
gpgv:  RSA key ID 2B90D010
gpgv: Good signature from "Debian Archive Automatic Signing Key (8/jessie) <ftpmaster@debian.org>"
gpgv:  RSA key ID 1A7B6500
gpgv: Good signature from "Debian Stable Release Key (9/stretch) <debian-release@lists.debian.org>"

Mirror [mirror11]: http://mirror.yandex.ru/debian/ stretch successfully added.
You can run 'aptly mirror update mirror11' to download repository contents.