I have certbot installed and successfully use it to encrypt my homepage.

Now i tried to setup an email system for my website using dovecot and postfix.

I got it mostly running, only problem is, that thunderbird gives me a warning about the adress being fraudulent because I use the ssl key of mysite.com for imap.mysite.com (same for smtp) So how can I add imap.mysite.com and smtp.mysite.com to the existing mysite.com certificate using certbot in order to avoid the warning?

1 Answer 1


You have to use the --expand option of certbot

--expand tells Certbot to update an existing certificate with a new certificate that contains all of the old domains and one or more additional new domains. With the --expand option, use the -d option to specify all existing domains and one or more new domains.

Example :

certbot --expand -d mysite.com,imap.mysite.com,smtp.mysite.com


  • thanks, ill check this off once I got it working Jan 3, 2020 at 10:45

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