Limits and quotas protect the Google infrastructure from an automated process that uses the Data Transfer API in an inappropriate way. Excessive requests from an API might result from a harmless typo, or may result from an inefficiently designed system that makes needless API calls. Regardless of the cause, blocking traffic from a specific source once it reaches a certain level is necessary for the overall health of the G Suite system. It ensures that one developer's actions cannot negatively impact the larger community.
In the unlikely event that your API request fails, you'll receive an HTTP status code response. A status code of 403 has error information about incorrect input, and an HTTP status code of 503 has error information indicating which API quotas have been exceeded. These responses allow your custom application to detect these errors and take appropriate action.
If your requests need to be completed in a fixed period of time, send your requests in parallel or use multiple threads in your Java or C# application. For example, break your requests by month or another time period. In the case of threads, try starting with 10 threads, one thread per request. Note, the thread recommendation has trade-offs and is not useful for all API situations. If the number of requests gets too high, quota errors will occur.
For all errors that are time based (maximum of N things for X seconds per thread), especially the 503 status code errors, we recommend your code catch the exception and, using an exponential backoff algorithm, wait for a small delay before retrying the failed call. A Data Transfer API example for one thread is to wait 5 seconds and retry the failed call. If the request is successful, repeat this pattern for the other threads. If the second request is not successful, your application should scale back on the frequency of the request until a call is successful. For example, increase the initial 5 second delay to 10 seconds and retry your failed call again. Also, decide on a retry limit. For example retry a request 5 to 7 times with different delay times before your application returns an error to the user.
|API Limit Categories||Limits|
|Queries per second (QPS)||The developer project limit is 10 queries per second (QPS) per account.|
|API Quota Categories||Quotas|
|Maximum API requests per day||The maximum API requests per day is 500,000.|
|Archive, expiration of messages||Group archives do not expire. Messages remain in an archive until the group is deleted. The email retention policy does not affect messages in a group's archive.|
|Mail message size||The maximum mail message size is 25MB. This limit includes the message's meta data headers, body, and any attachments.|
|Other Types of Limits||Limitations and Guidelines|
|Content type formats||An email message must be in the standard RFC 822 text format. A request's content type format for uploading migrated emails use the
|Data location policies||The API does not support data location policies requiring data be stored in specific geographic or political boundaries for contractual reasons. Do not use the API if data location is required for your account.|
|Parallel message insertions||The API supports parallel requests for email insertions into different group archives. But the API does not support parallel message insertions into the same group archive. Nor are batch requests supported in this version of the API.|
|Unauthorized requests||The API does not accept any unauthorized requests. A request is considered unauthorized if no authorization token is provided. For more information, see Authorizing Requests.|