Where to find textstring in Linux/Dovecot

Question

I have installed the iRedMail email server script on an Ubuntu 22.04 with Nginx.

Now, when I create a new email account, the user gets an email when he logs in the first time.  It’s a welcome email with a link to where you should login, but the link is totally wrong.  I have asked in the iRedMail forum, but all answer I got is that the installation doesn’t install anything to send out welcome messages.  I have tried to find the text string using grep, but it seems to hang and doesn’t show anything.  Can anyone hint about a better way to find this string?

root@mail:~# grep -r -i 'Welcome and thank you' /
grep: /proc/sys/fs/binfmt_misc/register: Invalid argument
grep: /proc/sys/net/ipv4/route/flush: Permission denied
grep: /proc/sys/net/ipv6/conf/all/stable_secret: Input/output error
grep: /proc/sys/net/ipv6/conf/default/stable_secret: Input/output error
grep: /proc/sys/net/ipv6/conf/eth0/stable_secret: Input/output error
grep: /proc/sys/net/ipv6/conf/lo/stable_secret: Input/output error
grep: /proc/sys/net/ipv6/route/flush: Permission denied
grep: /proc/sys/vm/compact_memory: Permission denied
grep: /proc/sys/vm/drop_caches: Permission denied
grep: /proc/kmsg: Resource temporarily unavailable

... explain – or even show – what’s wrong with the link.

Well, in the first place, there should not be a welcome message at all.  It’s nothing I have configured.  The welcome plugin in Dovecot is not enabled.  And, if it was to be correct, it should lead to the roundcube login mail.mxmail.pro/mail. This is the text:

Welcome and thank you for registering at Mx Mail! Your account has now been created and you can log in by using your email address and password by visiting our website or at the following URL: https://mxmail.pro/index.php? route-account/login&language=en-gb