An email alias passes mail sent to it on to a real inbox. Files travel inside the message, so a managed alias delivers attachments as well as text. Limits still apply. Managed services forward files up to a published size, and short-lived inboxes remove them before the message is shown. The type of alias and the limits along the route decide whether a file arrives.
How an attachment reaches an alias#
The MIME standard defines how a file travels inside an email. RFC 2045 was published on 1 November 1996 and sets out the format of internet message bodies, including multipart messages that hold a file next to the text. Binary data is encoded, usually in base64, so it can move inside a text message, and that encoding adds about a third to the file's size while it travels. The attachment is one part of the message, so it reaches the inbox when the message does.
An alias service takes the message in and sends the whole thing on to the destination inbox, parts intact. The guide to how email aliases actually work explains that mechanism, and the comparison of email forwarding and aliases explains how forwarding differs from a separate mailbox. A file that is inside the message when it reaches the alias is still inside it when it reaches the destination, unless a limit or a filter takes it out along the way.
Maximum message sizes#
Every managed alias service publishes a maximum message size, and the cap covers the whole message, attachments included. The published figures:
| Service | Maximum message size | Attachment handling |
|---|---|---|
| SimpleLogin | 25 MB | Forwarded with the message |
| addy.io | 25 MB, including attachments | Forwarded with the message, counts towards bandwidth |
| Firefox Relay | 10 MB | Forwarded with the message; 150 KB before March 2022 |
| Apple Hide My Email | No published limit | Mail forwarded to the personal inbox |
SimpleLogin puts its current limit at 25 MB in its FAQ and suggests a file upload service with a link for anything larger. addy.io says in its FAQ that forwarded mail and replies can carry attachments, that attachments count towards bandwidth, and that the maximum email size is 25 MB including attachments.
Relay's limit has changed once already. When Mozilla announced Relay Premium in November 2021, free Relay aliases came with attachments of up to 150 KB. Tickets and receipts ran over that limit, users reported it, and Mozilla raised it. A March 2022 announcement said the limit had gone up to 10 MB, so emails with or without attachments would reach the inbox. The two announcements sit on the Mozilla press blog, the 2021 announcement and the 2022 announcement, and Mozilla's support pages confirm 10 MB as the current limit. The 150 KB figure belongs to 2021, not to the service today.
Hide My Email has no published size figure. Apple's support page says mail sent to a Hide My Email address is forwarded to the personal email account, and gives no attachment size for the feature. The Apple support page for Hide My Email describes how the forwarding works.
A second limit waits at the destination inbox. For personal accounts Gmail caps messages at 25 MB, and a message over that cap has its attachment taken out and replaced with a Google Drive link. Google's support page on sending attachments in Gmail gives the 25 MB figure for personal accounts and notes that work and school accounts have limits set by the administrator. A message inside the alias service limit can still fail at an inbox with a lower one. Encoding narrows the margin further: a file of about 18 MB on disk is already close to a 25 MB encoded message. The lowest limit in the chain is the one that decides.
Short-lived inboxes#
Short-lived inboxes strip files, which is where the question matters most. Tmailor says on its own site that it takes the email in, then removes attached files and embedded images before storing the message, keeping only the text and a cleaned-up HTML version of the body. Nothing tells the sender the file was removed. What the reader sees is the subject, the sender and the body, with no file list, no download button and no note that something was taken out. Tmailor's article on attachments in short-lived inboxes covers the handling in full.
TempMailRoom gives the same result in its FAQ: file attachments are dropped and never stored, and emails larger than 1 MB in total are discarded entirely. Its inboxes last 10 minutes, and messages are permanently deleted when they expire. Both the attachment rule and the 1 MB limit come from the TempMailRoom FAQ. TempMailFast says attachments are not supported, while download links in the message body work normally, since a link is part of the text the inbox shows. Its article advises using an address under the reader's own control when the file only arrives as an attachment.
Temp-Mail.org is a reported exception, not a confirmed one. Tmailor's comparison table, checked against providers' official pages on 19 and 20 October 2026, says Temp-Mail.org accepts attachments and that its terms list downloading the message source including attachments. The claim comes from Tmailor's own comparison, not from Temp-Mail.org's own page, so it stands here as Tmailor's finding rather than a direct fact. Whether an inbox keeps attachments varies by provider, and the provider's own documentation is the place to check before relying on it for a file.
Embedded images and undocumented behaviour#
A picture pasted into the body of an email is not an attachment. Mozilla's support pages for Firefox Relay say only attachments are supported, and an image pasted into the body rather than attached is not forwarded. The same split applies elsewhere: a file sent as its own MIME part goes through, while content embedded in the HTML body may be treated differently.
No provider page checked for this article says what happens to a message over the size limit. SimpleLogin gives only the 25 MB limit, addy.io gives only the 25 MB limit, and Firefox Relay gives only the 10 MB limit. None of the three says whether an oversized message bounces back to the sender, is dropped without notice, or arrives without its attachment. No failure mode is claimed here that the providers do not document.
Files that need a lasting address#
Anything expected to arrive as a file needs a lasting alias or a real inbox, never a short-lived inbox. Receipts, tickets, statements and contracts are the usual cases. A booking confirmation carries its PDF ticket as an attachment, and it has to reach the inbox intact, which is why the guide to using email aliases for travel bookings uses a lasting alias. A shopping receipt is the same case. A statement or a contract may be needed months later, after a short-lived inbox has expired and its messages have been deleted.
Codes and links sit on the other side of the line. A two-factor code is text, and it reaches an alias as described in the article on receiving two-factor codes at an email alias. A confirmation link is text in the message body. The file is what decides: text and links pass through any inbox, while a file needs an address that forwards attachments.
Caution still applies to any file that does arrive. A file from an unknown sender can carry malware, and the article on opening email attachments safely covers the checks to run before opening one. An alias only delivers the file; it does not make it safe. A missing file was removed by a limit or a filter. A file that arrived from an unknown sender still needs checking before it is opened.
AliasFleet and attachments#
AliasFleet is a managed alias service. Mail sent to an AliasFleet alias is forwarded to the verified destination inbox with its attachments included as part of the message. That rests on the published full-message forwarding description and the bandwidth limit. No test attachment was sent through the live app for this article, so the claim is given on that basis rather than as a tested result.
The free tier gives 10 active aliases and 100 MB of monthly forwarding bandwidth, and attachments count towards that bandwidth because they are part of the forwarded message. The Pro tier gives 1 GB of monthly forwarding bandwidth, as listed on the pricing page. The pricing page lists the free tier as 10 active aliases, 1 verified destination inbox, 3 managed subdomains, 100 MB monthly forwarding bandwidth and two-way reply routing. AliasFleet is described in full on the AliasFleet homepage and in the article on what AliasFleet is.
There is no separate per-attachment limit on top of the bandwidth allowance. A message inside the monthly bandwidth is forwarded with its attachments, and a message over the destination inbox's own limit is subject to that inbox's rules, as with any forwarded mail. Replies can go out from the alias, so a conversation that starts with an attached file can continue without exposing the real address. An alias that starts receiving spam can be disabled in one click, as described in the guide on what to do when an alias starts getting spam.
