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Last modified by Alexandru Pentilescu on 2025/02/09 14:17
From version 7.1
edited by Alexandru Pentilescu
on 2024/05/19 14:20
Change comment: There is no comment for this version
To version 8.1
edited by Alexandru Pentilescu
on 2024/05/19 14:28
Change comment: There is no comment for this version

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81 81  Next is the "smtpd_relay_restrictions" which has a bunch of values assigned to it. The only one relevant to talk about is "permit_mynetworks", which informs Postfix that it's fine to relay any outgoing email from the IP addresses and hosts defined in the "mynetworks" variable, without having to authenticate them with user passwords.
82 82  Basically, this means that, as long as a service connects to port 25 of the current machine from an originating IP that's listed under "mynetworks" this means that Postfix will accept whatever email that service is trying to send and relay it over to its destination.
83 83  
84 +Please note though that the above configuration **still allows emails from external entities to be relayed through this server, as has happened recently to me when Gmail was sending spam through to my Postfix instance because it was trying to send an email to "pentilescu.com", a previous domain that I still own, the email wouldn't reach its destination because the SSL certificates were not configured for that specific domain anymore, the sending would get rejected, Google would automatically send a bounce email to the originator (i.e. my VPS) again, and this would cause the VPS to flood my inbox with these unwanted emails**, which can be abused by those with ill intents.
85 +
84 84  "mydestination = localhost" not sure about this one?
85 85  
86 86  "mynetworks" tells Postfix which machines are trusted. SMTP needs to trust sources of email before it can relay them. If you specify "permit_mynetworks" to "smtpd_relay_restrictions" then any machine whose IP is listed in this parameter can relay its email through this Postfix instance.
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118 118  
119 119  Finally, there's the "inet_interfaces" configuration parameter. This one specifies under which identities the current installation of Postfix will be assumed by the server. Postfix will accept all requests destined to any of these addresses as its own and will handle them.
120 120  
121 -In a docker configuration, assuming the services are using a "bridge" network driver, they will all have their own IP addresses in the aforementioned address space, and these addresses will be distinct from the proper address of the machine where Postfix is installed. As such, they need a target to resolve to reach the machine running Postfix. This target will be IP 172.16.0.1. When configuring each individual docker service, enter that IP as the IP of the SMTP server to use, as well as port 25, as its connection port. These should be the only parameters you should need to configure everything to work properly. 172.16.0.1 was a random address that I decided on. Really, it has no real relevance and can be changed to any private IPv4 address, whether in class B, C or A. The only point is that it should be reachable through this network driver.
123 +In a docker configuration, assuming the services are using a "bridge" network driver, they will all have their own IP addresses in the aforementioned address space, and these addresses will be distinct from the proper address of the machine where Postfix is installed. As such, they need a target to resolve to reach the machine running Postfix. This target will be IP 172.16.0.1. **IMPORTANT note: if you'll use TLS enabled in Postfix, please avoid using the raw IP address as mentioned here, as certain services like Nextcloud check the domain of the SMTP server against the TLS certificates being provided and, if they mismatch, it will reject the connection. This is why I added the "mail.transistor.one" hostname in there, as my TLS certificate is against all subdomains under *.transistor.one and, as such, can be verified successfully by it**. When configuring each individual docker service, enter that IP as the IP of the SMTP server to use, as well as port 25, as its connection port. These should be the only parameters you should need to configure everything to work properly. 172.16.0.1 was a random address that I decided on. Really, it has no real relevance and can be changed to any private IPv4 address, whether in class B, C or A. The only point is that it should be reachable through this network driver.
122 122  
123 123  = Instructing Postfix to relay emails through Google's servers, instead =
124 124  Assuming that running your own postfix server is a pain in the ass (especially since it's quite difficult to get DMARC or other authenticity mechanisms configured by yourself), a proper workaround for that is to simply rely on a third party emailing service to relay your emails for you.