Home / server / Questions / 343870
Accepted
Cerin
Asked: 2011-12-24 14:04:32 +0800 CST

Google SMTP Connection Timeout

  • 772

How do I find out why Gmail is seemingly refusing connections from my specific IP range?

I'm getting a "Connection timeout" error when attempting to send email through smtp.gmail.com using the email facilities in Django running on a Linux machine on Amazon's EC2 service.

Oddly, I can send mail using sendmail, but it initially gets the same timeout error and then falls back to an alternative server, which accepts a connection, e.g.

~$ echo -e "Subject:test subject\ntest body\n" | sendmail -v myuser@mydomain
Loading lookup modules from /usr/lib/exim/4.72-1.fc13/lookups
Loaded 0 lookup modules
LOG: MAIN
 <= app@domain U=app P=local S=443
Loading lookup modules from
/usr/lib/exim/4.72-1.fc13/lookups
Loaded 0 lookup modules
delivering 1ReChV-0001Hx-Ss
Connecting to aspmx.l.google.com [74.125.93.26]:25 ... failed:
Connection timed out (timeout=5m)
LOG: MAIN
 aspmx.l.google.com [74.125.93.26] Connection timed out
Connecting to ALT1.aspmx.l.google.com [173.194.66.26]:25 ... connected

This is only occurring from Amazon's cloud. I can connect to smtp.gmail.com from my localhost using the same credentials, and send email just fine. And I can ping smtp.gmail.com just fine from everywhere, so it doesn't seem to be a routing or firewall issue.

Google lists no problems on their status dashboard.

The server in question sends very low volumes of email (10-20 a day), so I'd be surprised if it was flagged for spamming.

linux smtp google gmail g-suite

4 Answers

  1. Sending email from an EC2 instance is just not a good idea unless you are handing the email to a mail server that has specifically agreed to accept your mail. There are a variety of reasons, but the main one is that an EC2's IP address is dynamic and a mail server must be on a static IP address to accept bounces.

    Basically, if you want to send mail, you need to send it to a real mail server that will take responsibility for delivering the mail to its destination. Amazon offers such services, with real mail servers hosted at static IP addresses.

    • 1

  2. Most of the times that I see similar problems with mail servers (and from the logs presented I understand that you connect to ALT1.aspmx.l.google.com but mail is not sent) disabling TCP Window scaling helps bypassing (not solving) the problem.

    I do not know what OS you're running on the EC2, but if it is Linux you may try adding:

    net.ipv4.tcp_rmem = 4096 87380 174760
net.ipv4.tcp_wmem = 4096 16384 131072
net.ipv4.tcp_window_scaling = 0

    in your /etc/sysctl.conf and run sysctl -p afterwards.

    • 1

  3. I've found Google has locked accounts/IP Addresses/ActiveSync etc when their automated protection systems suspect suspicious activity.

    ie, A user using Outlook with POP/SMTP suddenly can't log in with Outlook.

    To 'unlock' an IP, you can log into the GMail account from that IP using the website gmail.com, and the account will usually come good in a few minutes.

    Otherwise Google Tech Support once directed me to https://www.google.com/accounts/UnlockCaptcha or http://www.google.com/a/your_domain.com/UnlockCaptcha for an account that ActiveSync had locked down and nothing would bring it back.

    See here for more information: http://www.gmailhelp.com/2009/10/unlocking-googles-gmail-captcha/

    • 1
  4. Best Answer

    The problem has seemingly resolved itself. Since I could still send email using alternative Google servers, I suspect it was some minor networking issue between my server and Google.

    • 0