New "hard" rate-limits on API queries from 29 Mar 2012

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#1 Wed, 28 Mar 2012 11:11
Adam M

New "hard" rate-limits on API queries from 29 Mar 2012

The InterFAX API has had "soft" rate-limiting in place since its inception, as detailed under System Limitations. The "soft" limitation was not enforced until now in the case of the number of queries per minute that could requested from the InterFAX API for outbound fax status and for inbound fax retrieval.

Begininning 29 Mar 2012, InterFAX will impose "hard" rate limits by actively enforcing limitations on calls to the following Web Service methods:

Outbound methods
FaxStatus, FaxStatusEx, FaxStatusXML, FaxQuery, FaxQuery2

Inbound methods
GetList, GetList2.

This means that systems placing more than six calls per minute (subject to change; the authoritative number appears on the System Limitations page) to these methods will receive an error (code -1011), where they now receive a valid reply.

This change may or may not affect your application. Some applications may accept the error and retry the query after a while, while other applications may not handle the error gracefully. You are advised to check how your application behaves.

We are aware that making changes to a production API causes inconvenience to our clients, which is why we forcefully avoid making such changes during the normal course of business. However, in this case, over-usage of our API has in the recent weeks brought our system to a standstill on several occasions, which forces us to perform this change.

To avoid hitting the rate limit, apply the following practices when placing queries:


1. If you have a single outbound fax outstanding: simply query for its status no more than six times per minute.

2. If you have multiple outbound faxes outstanding: query for all faxes at once, for example by using method FaxQuery with the "IN" verb and all the outstanding transaction IDs in "VerbData".

3. If you have more than 100 faxes outstanding, use method 2 above, querying for 100 faxes at a time.

4. If you have no outbound faxes outstanding, avoid querying the Web Service. (Yes, you'd be surprised that some applications keep on querying for faxes when none are outstanding).

5. Alternatively, avoid polling for outstanding faxes and use outbound confirmation callback


1. Use method GetList or GetList2 no more than six times per minute.

2. Even better: avoid polling altogether and set up inbound callback.

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