I have setup Postfix on Ubuntu 16.04 and cannot receive mail.

I'm assuming you pointed a hostname at your linode IP - what happens when you try to deliver mail to it? Do you get a bounce at the source?

Can you tail the postfix logs? The file is usually called /var/log/maillog, /var/log/mail, or something similar

Eg: mail.example.com A 192.0.0.1
example.com MX mail.example.com

Are there any network filters preventing me from receiving email?

In general, unless you have been informed otherwise due to special circumstances, there are no network filters in place for your Linode.

You can verify that there are no external filters in place for your Linode by checking the port 25 of your Linode and see that it is responding:

…
telnet 192.0.2.143 25
Trying 192.0.2.143…
Connected to li1###-##.members.linode.com.
Escape character is '^]'.
EHLO
220 example.com ESMTP Postfix (Ubuntu)
501 Syntax: EHLO hostname
QUIT
221 2.0.0 Bye
Connection closed by foreign host.
…

The following is a guide on debugging Postfix, if you have any questions about what you read here, please let us know and we will try to clarify:

• http://www.postfix.org/DEBUG_README.html

We also provide the following guide on a common Postfix setup:

• https://www.linode.com/docs/email/postfix/troubleshooting-problems-with-postfix-dovecot-and-mysql/

• https://www.linode.com/docs/email/postfix/

Postfix rarely works alone to provide mail services. Can you describe your setup?

• Was there a guide that you used to setup your mail services?
• Could provide the contents of your main.cf file?
• What is the domain for which you are trying to receive email
• How have you setup your DNS records, especially your MX records.

Some places to check:

DNS

Ensure that your domain provides MX records that point to your Linode:

$ dig -tMX example.com
...
example.com.    21599   IN  MX  10  example.com.
example.com.    21599   IN      MX      10  mail.example.com.

$ dig example.com

example.com.       21599   IN      A    192.0.2.143

$ dig example.com

mail.example.com.   21599   IN      CNAME  example.com.

System Mail Name

Make sure your system mail name in your main.cf is your domain for your email and not your hostname. i.e. example.com, not mail.example.com

Mail Users

Make sure you have created the users that will receive mail. For example:

sudo adduser exampleuser

I hope this helps to get you started.