makeacceptmailfor reads /etc/courier/esmtpacceptmailfor.dir and creates /etc/courier/esmtpacceptmailfor.dat which is a binary database file. /etc/courier/esmtpacceptmailfor.dat is a list of domains that the Courier mail server accepts mail for, via ESMTP. /etc/courier/esmtpacceptmailfor.dir is a subdirectory containing one or more files. Each file in this subdirectory is plain text file, containing a list of mail domains, one per line, in lowercase. All files in the subdirectory are concatenated, and the binary database file is created from the result. Note that this build of courier ignores any files that match the regex pattern ".*.dpkg-[a-z]*" (dpkg configuration file handling) and ".*~" (backup files of some editors).
The makeacceptmailfor can be executed while the Courier mail server is running, and any changes take effect immediately. However, only one instance of makeacceptmailfor can be executed at the same time.