why gmail smtp reply message size limit is different

Salar

11/19/23, 12:10 PM

According to google documentations with following link https://support.google.com/a/answer/1366776?hl=en , message size limitation for inbound emails is 50 MB but as i was testing gmail smtp server there was a reply as follow:

220 mx.google.com ESMTP p14-20020a7bcc8e000000b003c6f289e99esi5592406wma.88 - gsmtp
ehlo test.com
250-mx.google.com at your service, [46.209.208.220]
250-SIZE 157286400
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8

From above output it is saying that gmail.com mail server is accepting up to 150 MB so my question is what is the correct limit ? and why the smtp response is different ?

131

2 + 1

email-server

smtp

gmail

Gerald Schneider

11/19/23, 12:20 PM

You would need to ask someone at Google.

Score:3

Server

joeqwerty

11/19/23, 4:17 PM

Your test has determined the maximum message size that the servers at mx.google.com will receive, but those servers aren't likely hosting the actual user mailboxes. The servers at mx.google.com sit at the ingress for inbound email and then pass that email onto the servers that host the actual mailboxes. The servers that host the actual mailboxes may limit the maximum inbound message size to 50MB, or it may be that the mailboxes themselves restrict the maximum inbound message size to 50MB. You haven't discovered a contradiction in Google's terms. You've merely discovered the maximum message size that the servers at mx.google.com will receive.

What you've discovered is common. The servers at the ingress are configured for the maximum inbound message size that the email system as a whole will accept. Those message size limits can, and often are, then further limited internally, dependent upon where the email is destined. It's not uncommon to see SMTP servers at the ingress of the email system set to a specific size limit and then to have the mailbox hosting servers or mailboxes themselves configured for a lower message size limit.

+ 0

Score:1

Server

anx

11/19/23, 1:09 PM

The limit is whatever they do accept and is likely to have changed and change again, so for a current answer on that just try it or ask Google.

As to why someone would document a different limit than what their MX say in the SMTP session: If they announce a larger limit than what they are willing to accept later on, they can

apply a consistent limit to 7-bit and 8-bit transfer (which is nice to reduce confusion with senders expecting to be always able to send 50MiB, regardless of transfer-encoding overhead) and they can
have their help page URL from their SMTP response (eg. 550 5.7.1 https://support.google.com/mail/answer/6584) appear in the non-delivery notification, which won't happen if the sending server gives up right away.

+ 0

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: why gmail smtp reply message size limit is different

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.