Hi Nali. There could be several reasons why you are seeing 601 errors. The most common are DNS issues and firewall issues. Have you tried to change the DNS servers that SM uses to either Google or CloudFlare's DNS servers? My suggestion would be to try that first and let us know if that resolves it. If not, there are a few other places I think I can point you. Thanks.
Linda Pagillo
Mail's Best Friend
Email: linda.pagillo@mailsbestfriend.com
Web: www.mailsbestfriend.com
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