All email connections (spam and not spam) to a domain are logged to the logging server. To make sure a connection can be logged, the "RCP TO" information needs to have been received. Connections are generally only temporarily or permanently rejected after receiving this "RCPT TO" data, to ensure all connections being available from the logging system. Connections may not be logged whenratelimiting is applied because of a flood of connections from a certain IP, or when the sending server is violating certain requirements from the RFC 5321.
You can search the log under the 'Log Search' link:

Storage period
The connections logged are accessible for up to 28 days. We may store the data securely in an archived format up to 550 days.
Access
The logs can be easily downloaded or searched from the webinterface.
Delay
The logging data is processed every 10 minutes on all filtering nodes. The average delay for the connections to be visible in the log search is therefore 5 minutes.
Timezone
The raw log file download is always in UTC. The log search presents the time in the timezone set on the Settings page of the admin control panel.