There are two bugs that I currently aware of regarding the sendmail boot process. The first and simplest deals with your hostname. In Ubuntu, the default configuration of sendmail and apache required a fully qualified domain name. You can adjust your FQDN manually in the /etc/hostname file. The proper format is:
name.domain.com
Save the file, and you will not get any errors on an apache or sendmail reboot. Also there is sometimes an issue when sendmail tries to reconfigure its cf file during boot. I don’t experience this issues, but its worth mentioning due to its simple workaround. Just delete the two following files, and sendmail will not re-configure on boot (you will have to do it manually if you change its settings):
/etc/network/if-down.d/sendmail
/etc/network/if-up.d/sendmail
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On Fedora, the system configuration requests a domain name and a hostname separately. On Ubuntu it requests only the hostname, in which you would input your hostname.domain. On Debian it also requests only a hostname, in which you would also type hostname.domain.
On Ubuntu and Fedora you can reference your computer just by the hostname. I have noticed that on Debian, an SSH connection will show the host computer as the hostname.domain. There is nothing to be worried about, this is just some observations about the behavior of different Linux distributions.
Note that on Debian systems, you cannot use a short hostname, you need the hostname.domain to establish a FQDN (Fully Qaulified Domain Name). To set the hostname use:
sudo hostname -v hostname.domain
For instance, the web server, that produces this website, uses a hostname of web.bgevolution.com, where web is the hostname and bgevolution.com is the domain name. At one point I tried to just use the hostname as web, without the domain, and by not setting the domain, Apache was setting 127.0.0.1 as the FQDN. I dont think this is an issue at all, as Apache fully functioned properly, but none the less I dont like to see errors when I restart a computer service, therefore I set the hostname to include a domain to establish a FQDN 
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