Email Limits and Restrictions When Using Plusnet SMTP Servers

[#1]

@ashburnhamins 

I asked earlier...

It is not clear from your description if your web based form is SENDING the email via its own SMTP or SUBMITTING the email to your own SMTP, that is Plusnet.  It is more usual for web forms to use their own SMTP service and simply email the form to your mail box.

I cannot discern a clear answer in the succeding responses and from the comments made, I am suspecting that there is more than one thing being done here.

Sending data entered in a form (one item sent to a sinlge address) on a website does not sound the same as sending a 'batch' which implies one item sent to multiple addressees.

I think it would help if you can provide a bit more detail on what you are doing, from where and how it is configured.

Usually a form on a website uses something like FormMail to send the completed from "home" to the website owner.  Such configurations would use a local SMTP service.

Other technologies might seek to talk direct to a SMTP service - does your 1&1 account afford access to 1&1's SMTP server? Using that would side step Plusnet's pragmatic anti-spam measures.

[#2]

@Townman 

Sorry for any confusion caused, I'll try and explain from the beginning what we are doing here:

We send emails via two methods as follows:
1) In-house (UK based), via PC based Outlook program, using Plusnet internet connection, using Plusnet SMTP settings.
2) Via a web-form on our website which is hosted with 1&1 (which seems to based in Germany), website connects to Plusnet SMTP using same settings as method 1 (yes we know 1&1 have their own mail servers we can use and we have been using them for years but they have been unreliable recently so we have made a decision to use an alternative provider)

We have not had any issues thus far with method 1 and we are also using method 2 regularly with no issues. However, method 2 failed once when we sent approximately 40 messages in a 2 minute period. These were 40 individual messages each sent to single recipient (all recipients different though) all sent one at a time. We received about 15 error messages which related to the last 15 emails sent from these 40 (the first 25 therefore going through fine). Each error said "SMTP Error: Too many rcpts in time period from this IP" which suggests we hit a sending limit.

Ignore my use of batch - my fault for using poor wording to describe what we are doing. We are only ever sending single transactional emails to single recipients and sent one at a time. Like I say, everything is working fine for both these methods apart from this one time when we sent a few of these in a short space of time.

[#3]

Thank you for the confirmation of what I suspected could be the case. Always best to be certain!!

It looks like there could be an issue with the 40 per hour limit (total per hour or at the rate of, are not the same). Hopefully @JW can clarify.

[#4]

There's a couple of things that could have been the cause of this particular issue. The first is if the originating IP is shared between a few users, it's possible that someone else could have been attempting to send emails within the same 60 minute window and caused the counter to increment. The other potential cause would be that particular IP, or range of IPs, being given a lower allowance due to either their perceived reputation or geographic location.

[#5]

@JW It would have been very coincidential if it is to do with a shared IP as this issue only happened during that little spike of 40 emails we sent and has been fine before and since. It cannot be ruled out though. The lower allowance seems more logical but would be nice to know if it actually does exist and exactly what it is per min/hour?

[#6]

@JW 

Do you have any insight as to how the metric works please?

It is...

1. Up to 40 within the last 60 minutes?
2. Not more than one in the last 90 seconds?

The first gives a number per hour, which could all be sent within one minute, the second gives an "at the rate of per hour" metric.

Your answer above somewhat suggests that the rate limitations are based on the sending IP address, rather than the submitting account, which is a very different perspective to what has been widely implied over the years.  The parlance used has somewhat implied that the limitation was applied to the submitting mailbox name.

@ashburnhamins 

In your spot test of a batch of 40, one has to consider what happened in the 60 minutes preceding the test.

[#7]

In your spot test of a batch of 40, one has to consider what happened in the 60 minutes preceding the test.

@Townman I would be unable to give exact numbers but I would be suprised if I sent more than 20 emails in the 60 mins leading up to the batch of 40. Once again, all sent to one recipient and would have been randomly spread in terms of time.

If we use these figures, that is 60 sent in an hour. From this I got 15 error messages so 45 got through in an hour.

I'll re-iterate that these are rough figures but gives you a ballpark of the numbers we might be talking here.

[#8]

@Townman 

Without going into too much detail about the inner workings of the platform, we can't reveal everything as it then becomes less effective, most of the metrics are based on a 60 minute window. If you want to send all of your emails in the first 5 minutes that's fine, provided your connection and software can handle that volume.

As for it being tracked based on the IP or submitting account, as most customers won't be authenticating we do track some metrics on the submission IP address.

[#9]

@JW 

Thank you that is really helpful.  However...

As for it being tracked based on the IP or submitting account, as most customers won't be authenticating we do track some metrics on the submission IP address.

Surely if access is not from within the Plusnet network, authentication is mandatory?  Therefore off-network connections (within the UK or over seas) MUST be authenticated.  In which case overseas access should be predicated solely on submitting account.  IP tracking then becomes a matter of looking at abuse from UK connected users on the Plusnet network.

@ashburnhamins 

The answers suggest that the metric is around 40 from an over seas IP address in a 60 minute (I guess rolling) window.  If you do not anticipate the form being submitted more than 40 times an hour, you don't have a problem.

If you do, you have two solutions - either use the 1&1 SMTP server to do the submissions or ask 1&1 to host your service on a UK platform.

HTH?

[#10]

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@Townman wrote:

@JW 

Thank you that is really helpful.  However...

As for it being tracked based on the IP or submitting account, as most customers won't be authenticating we do track some metrics on the submission IP address.

Surely if access is not from within the Plusnet network, authentication is mandatory?  Therefore off-network connections (within the UK or over seas) MUST be authenticated.  In which case overseas access should be predicated solely on submitting account.  IP tracking then becomes a matter of looking at abuse from UK connected users on the Plusnet network.

@Townman 

Yes, if the connection is from outside of our network then authentication is required. Though given the potential for abuse if a bad actor manages to obtain a group of valid credentials, there have to be levels of mitigation in place.

[#11]

Okay, I may be getting this wrong but this is how I am surmising:

There are 3 levels of restriction:

1. 1,000 per hour while sending on the Plusnet network
2. 300 per hour while off the Plusnet network (as per @JOLO talking about this post here)
3. 40 (approx) per hour while sending off the Plusnet network and on a particular IP, or range of IPs, being given a lower allowance due to either their perceived reputation or geographic location (as per @JW)

If you do, you have two solutions - either use the 1&1 SMTP server to do the submissions or ask 1&1 to host your service on a UK platform.

@Townman If what I'm saying above is right then getting 1&1 to move me to a UK server may help, but if the it is due to perceived reputation of their IP(s) rather than geolocation then this may not change the lower allowance.