Open port 25 (SMTP)

Question

Open port 25 (SMTP)

R Cinezi 0

Dear Sir/Madam,

I would like to request that port 25 (SMTP) be opened for sending emails on a virtual machine hosted on Microsoft Azure.

We recently deployed a SmarterTools email server on a VM in Azure. The internal configuration of the operating system and the VM's firewall has already been properly adjusted to allow traffic on port 25; however, we have identified that the blockage occurs at the platform level.

Therefore, we kindly request:

The opening of port 25 for outbound traffic (Outbound SMTP), or

If this is not possible, guidance on the necessary procedure (e.g., unblocking request, use of an authenticated relay, or alternative requested by Azure).

We remain available to provide any additional information that may be necessary, such as subscription ID, VM name, region, or justification for use.

Thank you in advance for your attention and I await your guidance.

The VM is located at the account "PII" with business access. The machine is called smartermail.

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Answer 1

Andreas Baumgarten 131.2K MVP Volunteer Moderator

Hi @R Cinezi ,

sending emails using Port 25 (SMTP) is blocked in Azure by default.

The preferred method to send emails is to use a authenticated SMTP relay services (Port 587), for instance the Azure Communication Services.

Source: https://learn.microsoft.com/en-us/troubleshoot/azure/virtual-network/troubleshoot-outbound-smtp-connectivity#recommended-method-of-sending-email

(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)

Regards

Andreas Baumgarten

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Answer 2

Hi @R Cinezi,

Thank you for reaching out on Microsoft Q&A forum.

Outbound SMTP traffic on TCP port 25 from Azure virtual machines is controlled at the Azure platform level and depends on the subscription type being used. Could you please confirm which subscription type this VM is running on (Enterprise Agreement (EA), Microsoft Customer Agreement for Enterprise (MCA‑E), Enterprise Dev/Test, Pay‑As‑You‑Go, CSP, etc.)?

For standard Enterprise Agreement (EA) and MCA‑E subscriptions, outbound SMTP connections on port 25 are not blocked by Azure. However, email delivery is not guaranteed, as external mail providers may still reject or filter emails sent directly from Azure IP ranges.

For Enterprise Dev/Test subscriptions, outbound SMTP on port 25 is blocked by default, but an exemption can be requested. This can be done from the Azure Portal → Virtual Network → Diagnose and Solve Problems → “Cannot send email (SMTP‑Port 25)”. If the subscription qualifies, the exemption is applied automatically. After approval, the affected VMs must be stopped, deallocated, and started again for the new network policy to take effect.

For all other subscription types, outbound SMTP on port 25 remains blocked by design and cannot be unblocked. In these cases, Microsoft recommends using an authenticated SMTP relay (for example, Azure Communication Services Email, Microsoft 365 SMTP relay, or third‑party providers) over port 587, which is not restricted in Azure.

This restriction exists to protect the Azure platform and its IP reputation and to comply with industry anti‑spam standards.

Refer: https://learn.microsoft.com/en-in/troubleshoot/azure/virtual-network/troubleshoot-outbound-smtp-connectivity

Once we have the subscription type, we can confirm eligibility and advise on the next steps.

Kindly let us know if the above helps or you need further assistance on this issue.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Open port 25 (SMTP)

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