A colleague claims to have sent their report before midnight, yet your inbox shows the date of the following day. This seemingly trivial discrepancy can pose a real problem during a dispute, an application, or a contractual exchange. Knowing the exact time of sending and receiving an email requires looking in the right place, well beyond the visible timestamp in your messaging system.
Technical headers of an email: the only reliable source for the sending time
The time displayed in your inbox is just a summary. The true timeline of the message is hidden in its Internet headers (sometimes referred to as “full headers” or “message source”). These lines of text, automatically added by each server traversed, constitute the mail’s log.
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Two fields deserve your attention. The Date: field corresponds to the timestamp recorded by the sender’s software at the moment they click “Send.” The Received: fields, on the other hand, are added by each relay server. Each Received line indicates the time at which the server took charge of the message, as well as the name of the concerned server.
To find out how long it takes for an email to arrive according to Astuces Business, you need to compare the first Received line (sending server) and the last one (receiving server). The gap between the two gives the actual transit time.
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Have you ever noticed that the times in these headers sometimes seem inconsistent? It’s often a matter of time zone. Servers record the time in UTC (Coordinated Universal Time), while your messaging system displays it in your local time zone. An email “sent at 11 PM” in UTC becomes “1 AM” in French time during winter.
Display the exact reception time in Gmail, Outlook, and Thunderbird
The procedure to access the headers varies depending on the email client. Here are the three most common cases.
Gmail (web browser)
Open the message. Click on the three vertical dots to the right of the reply area, then select “Show original.” A new window opens with all the headers. Gmail also displays a summary at the top of the page with the Date, SPF, and DKIM fields.
In the message list, Gmail only displays the time for today’s emails. For an older message, you need to open it: the full date and time then appear when hovering over the date displayed next to the sender’s name.
Outlook (desktop application)
Open the message in a separate window. Go to File, then Properties. The “Internet headers” box contains all the Received lines. On Outlook web (OWA), click on the three dots, then “View message source.”
Thunderbird
Thunderbird displays the full headers via View, then Message Source (shortcut Ctrl+U). All the Received lines appear in reverse chronological order: the first line at the top corresponds to the last server, the one that delivered the message to your inbox.
Reliability of timestamps: what the header does not guarantee
Reading the headers is not always enough. One rarely discussed point deserves your attention: the Date: field can be falsified by the sender. A misconfigured email client, a skewed system clock, or deliberate manipulation can produce a misleading timestamp.
The Received fields added by recognized email servers (Google, Microsoft, OVH) remain more reliable, as the sender does not directly control them. If you have doubts about the authenticity of a timestamp, focus on the Received lines rather than the Date field.
Another limitation: the journey of an email is not linear. A message can transit through several relay servers, with variable queues. The transit time depends on the availability of the servers, and an email can remain pending for several minutes on an overloaded relay before being forwarded to the next one.
Email open trackers: why the reading time has become approximate
Knowing the sending and arrival time is one thing. Knowing when the recipient actually read the message is another. Tracking tools (trackers) insert an invisible image into the body of the email. When the recipient opens the message, the image loads, and the tracker records the time.
This technique has lost precision in recent years. Anti-tracking protections have become widespread:
- Apple Mail Privacy Protection preloads images remotely, triggering false open notifications without the recipient having read anything
- Gmail caches certain images on the server side, masking the actual time of consultation by the user
- Several browser extensions and email settings purely block the loading of remote images
The opening time reported by a tracker is no longer a reliable data for establishing the exact moment of reading. It remains useful for overall trends (marketing campaigns, open rates), but not to prove that a specific person viewed a message at a given time.
Time zone and display time: the setting that everyone forgets
Modern webmails allow you to choose the display time zone in the account settings. If this setting does not match your actual location, all displayed times will be offset, without the headers being at fault.
Here are some useful checks before concluding that there is a timestamp issue:
- In Gmail, check the time zone in Settings, then General, then Time Zone
- In Outlook, the time zone is set in the regional options of the Microsoft account or in the Windows settings
- Always compare the time of the Received headers (in UTC) with your local offset to eliminate any ambiguity
Set your email time zone to your actual area before comparing timestamps. A one or two-hour difference on a contractual email can create a costly misunderstanding.
The time of an email is never as simple as a number displayed in an inbox. The Received headers remain the most solid technical reference, provided you know how to read them and take into account the UTC time zone. For anything related to proof of sending or receiving, that’s where you need to look, not in your messaging summary.