Why I Switched From Gmail to Brevo for All My Homelab Email Alerts

· HomelabDevOps

How and why I migrated all my homelab email alerts — Proxmox backups, Zabbix monitoring, and even an ESP32 door sensor — from Gmail App Passwords to Brevo's SMTP relay.

I run a fairly typical homelab: three Proxmox servers, a Zabbix monitoring instance, and a handful of IoT devices. They all need to send email alerts — backup reports, threshold warnings, door sensor notifications. For years, I used Gmail with App Passwords for this. Last week, I ripped it all out and switched everything to Brevo (formerly Sendinblue). Here’s why.

The Problem With Gmail

Gmail’s SMTP server (smtp.gmail.com) works fine for casual use, but it has some serious pain points when you’re running it across multiple servers and devices:

1. Authentication Failures and Bounces

Gmail has been tightening its sending policies. My Proxmox servers were trying to send directly to Gmail’s MX servers, and every single email was getting bounced:

550-5.7.26 Your email has been blocked because the sender is unauthenticated.
Gmail requires all senders to authenticate with either SPF or DKIM.

My servers use .local hostnames (e.g. your-server.local), so there’s no SPF or DKIM to speak of. Gmail was rejecting everything.

2. App Password Management

Each service needs its own App Password. Across three Proxmox nodes, Zabbix, Netdata, and an ESP32, that’s a lot of credentials to manage. If Google decides to revoke them (which happens), you’re scrambling to regenerate and update them everywhere.

3. IPv6 Rejection

Even when authentication was configured, Gmail was rejecting emails sent over IPv6 because my residential IP doesn’t have proper PTR records:

550-5.7.1 Gmail has detected that this message does not meet IPv6 
sending guidelines regarding PTR records and authentication.

4. Sender Address Limitations

With Gmail, your sender address must be your Gmail address. You can’t send from proxmox-alerts@yourdomain.com — it’ll always show as your personal Gmail in the recipient’s inbox.

Why Brevo?

Brevo (formerly Sendinblue) is a transactional email service with a generous free tier — 300 emails per day — which is more than enough for homelab alerts. Here’s what made it the right choice:

  • Proper SMTP relay — Your servers authenticate with Brevo, and Brevo handles the delivery with proper SPF, DKIM, and DMARC. No more Gmail bounces.
  • Custom sender addresses — I can send from proxmox-alerts@yourdomain.com, zabbix-alerts@yourdomain.com, and door-alerts@yourdomain.com. Each service gets its own identity.
  • One set of credentials — One SMTP key works across all my servers. Or I can generate separate keys per service for better security isolation.
  • No IPv6 issues — Brevo’s relay servers handle delivery over their own well-configured infrastructure.
  • Works everywhere — Standard SMTP on port 587 with STARTTLS. Works with Postfix, Zabbix, ESP32, anything that can speak SMTP.

What I Migrated

Proxmox Servers (node1, node2, node3)

All three Proxmox nodes now relay through Brevo via Postfix. The configuration is identical across all three (minus the hostname):

/etc/postfix/main.cf — key additions:

relayhost = [smtp-relay.brevo.com]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = encrypt
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
sender_canonical_maps = hash:/etc/postfix/sender_canonical

/etc/postfix/sasl_passwd:

[smtp-relay.brevo.com]:587 your-brevo-login@email.com:YOUR_BREVO_SMTP_KEY

/etc/postfix/sender_canonical — rewrites the From address:

root@your-server.local proxmox-alerts@yourdomain.com
root proxmox-alerts@yourdomain.com

After running postmap on both files and restarting Postfix, backup notifications started flowing immediately.

Gotcha: On two of my servers, the libsasl2-modules package wasn’t installed, which caused a “no mechanism available” SASL error. A quick apt install libsasl2-modules fixed it.

Zabbix

Zabbix has its own built-in SMTP client, so no Postfix configuration was needed. I just updated the Email media type settings:

Setting Value
SMTP Server smtp-relay.brevo.com
Port 587
Security STARTTLS
Authentication Username + SMTP Key
Sender zabbix-alerts@yourdomain.com

ESP32 Door Sensor

I have an ESP32 with a reed switch that emails me when a door opens or closes. The Arduino sketch uses the ESP_Mail_Client library, so the change was straightforward:

#define SMTP_HOST "smtp-relay.brevo.com"
#define SMTP_PORT 587
#define AUTHOR_EMAIL "your-brevo-login@email.com"
#define AUTHOR_PASSWORD "YOUR_BREVO_SMTP_KEY"
#define SENDER_EMAIL "door-alerts@yourdomain.com"

The key difference from the Gmail version: Brevo uses port 587 with STARTTLS instead of port 465 with SSL, and you can set a separate sender address from the authentication email. I’ve published both versions (Gmail and Brevo) in my ESP32 Reed Sensor Email Notifier repo.

The Result

All my alerts now arrive reliably from clean, identifiable sender addresses:

  • proxmox-alerts@yourdomain.com — Backup reports from all three PVE nodes
  • zabbix-alerts@yourdomain.com — Monitoring threshold alerts
  • door-alerts@yourdomain.com — ESP32 door sensor notifications

No more Gmail bounces, no more “sender unauthenticated” errors, no more managing multiple App Passwords. The migration took about an hour across all services.

Tips If You’re Doing This

  1. Verify your sender domain in Brevo — Add your domain in Brevo’s settings and set up the DNS records (SPF, DKIM). This ensures your emails don’t land in spam.

  2. Install libsasl2-modules on Debian/Ubuntu servers — Postfix needs this for SASL authentication. It’s not always installed by default.

  3. Run newaliases after editing /etc/aliases — If you’re seeing “alias database unavailable” errors in your mail logs, this is probably why.

  4. Use postqueue -f to flush stuck emails — After fixing your Postfix config, flush the queue to retry any deferred messages.

  5. Keep your SMTP keys separate — Generate different Brevo SMTP keys for different services. If one gets compromised, you only need to rotate that one key.

  6. 300 emails/day is plenty — For a homelab, you’ll rarely hit this. My three Proxmox nodes backing up 16+ VMs each, plus Zabbix alerts, use maybe 20-30 emails on a busy day.

If you’re still using Gmail App Passwords for your homelab alerts, I’d strongly recommend making the switch. Brevo’s free tier is generous, the setup is minimal, and the reliability improvement is immediate.