{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,15]],"date-time":"2026-06-15T06:55:27Z","timestamp":1781506527568,"version":"3.54.1"},"reference-count":27,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2026,6,12]],"date-time":"2026-06-12T00:00:00Z","timestamp":1781222400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Network"],"abstract":"<jats:p>This paper presents an organization-managed IMAP Agent framework for extending email functionality in environments that rely on outsourced mail services. In this study, outsourced mail services refer to externally operated mailbox providers offering sufficiently scalable email infrastructures and standard IMAP interfaces, such as Gmail, Microsoft 365, and other commercial mailbox providers. In the proposed framework, IMAP Agents are operated within an organization, while user authentication continues to rely on existing institutional infrastructures such as Identity Providers (IdP) or Integrated Authentication Infrastructure (IAI). The IMAP Agent operates as a post-authentication processing component using credentials issued by these infrastructures, without modifying or intervening in the outsourced mail service itself. The framework enables organization-managed mailbox-side email processing without requiring administrative control over the mail server or dependence on provider-specific APIs. As a proof of concept, representative email-processing functions are implemented, including detection of suspicious messages based on header-level authentication information and automatic insertion of thread-consistent warning messages without altering the original email content. To evaluate the feasibility of the proposed framework, a prototype system was implemented using multiple containerized IMAP Agent instances. The experimental results showed that warning messages were typically appended within approximately 300 ms after message detection. Multi-container evaluations ranging from 1 to 100 concurrent IMAP Agent instances demonstrated low CPU overhead and approximately linear memory growth under idle-monitoring conditions, indicating the operational feasibility of deploying multiple IMAP Agent instances on a single host. These results suggest that the proposed framework can provide provider-independent and organization-managed extension of email functionality in outsourced mail environments through standard IMAP operations.<\/jats:p>","DOI":"10.3390\/network6020039","type":"journal-article","created":{"date-parts":[[2026,6,15]],"date-time":"2026-06-15T05:59:47Z","timestamp":1781503187000},"page":"39","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["An IMAP Agent Framework for Extending Email Functionality in Outsourced Mail Services"],"prefix":"10.3390","volume":"6","author":[{"ORCID":"https:\/\/orcid.org\/0009-0000-3779-0390","authenticated-orcid":false,"given":"Xiuyuan","family":"Chen","sequence":"first","affiliation":[{"name":"Department of Electronic and Information Engineering, Tokyo University of Agriculture and Technology, Koganei 184-8588, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4964-802X","authenticated-orcid":false,"given":"Tomoaki","family":"Tsutsumi","sequence":"additional","affiliation":[{"name":"Institute of Humanities and Social Sciences, University of Tsukuba, Tsukuba 305-8577, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5072-298X","authenticated-orcid":false,"given":"Rei","family":"Nakagawa","sequence":"additional","affiliation":[{"name":"Division of Electrical Engineering and Computer Science, Institute of Engineering, Tokyo University of Agriculture and Technology, Koganei 184-8588, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2967-5557","authenticated-orcid":false,"given":"Yong","family":"Jin","sequence":"additional","affiliation":[{"name":"Center for Information Infrastructure, Institute of Science Tokyo, Meguro 152-8550, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2651-2701","authenticated-orcid":false,"given":"Nariyoshi","family":"Yamai","sequence":"additional","affiliation":[{"name":"Division of Electrical Engineering and Computer Science, Institute of Engineering, Tokyo University of Agriculture and Technology, Koganei 184-8588, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,6,12]]},"reference":[{"key":"ref_1","unstructured":"Oberlo (2026, June 04). Email Usage Statistics 2024. Available online: https:\/\/www.oberlo.com."},{"key":"ref_2","unstructured":"Klensin, J. (2026, June 04). Simple Mail Transfer Protocol. RFC 5321. Available online: https:\/\/www.rfc-editor.org\/info\/rfc5321."},{"key":"ref_3","unstructured":"Gellens, R., Newman, C., and Lundblade, L. (2026, June 04). POP3 Extension Mechanism. RFC 2449. Available online: https:\/\/www.rfc-editor.org\/info\/rfc2449\/."},{"key":"ref_4","unstructured":"Melnikov, A., and Leiba, B. (2026, June 04). Internet Message Access Protocol (IMAP)\u2014Version 4rev2. RFC 9051. Available online: https:\/\/www.rfc-editor.org\/info\/rfc9051\/."},{"key":"ref_5","unstructured":"Crispin, M. (2026, June 04). Internet Message Access Protocol\u2014Version 4rev1. RFC 3501. Available online: https:\/\/www.rfc-editor.org\/info\/rfc3501\/."},{"key":"ref_6","unstructured":"Google (2026, June 04). Gmail API. 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Use of SRV Records for Locating Email Submission\/Access Services. RFC 6186. Available online: https:\/\/www.rfc-editor.org\/info\/rfc6186\/."},{"key":"ref_12","unstructured":"Yamai, N., Kitagawa, N., and Yokogi, K. (2020). E-Mail Processor and Programs. (Japan Patent JP6757028B2), Available online: https:\/\/patents.google.com\/patent\/JP6757028B2\/ja."},{"key":"ref_13","unstructured":"Leiba, B. (2026, June 04). IMAP4 IDLE Command. RFC 2177. Available online: https:\/\/www.rfc-editor.org\/rfc\/rfc2177."},{"key":"ref_14","unstructured":"Crispin, M. (2026, June 04). Internet Message Access Protocol\u2014Version 4rev1. RFC 2060. Available online: https:\/\/www.rfc-editor.org\/info\/rfc2060\/."},{"key":"ref_15","unstructured":"Tashiro, K., Yamai, N., and Naoya, K. (2019). Flexible Email Forwarding System Using IMAP Agent Without Changing Server Configuration. Proceedings of the DICOMO2019, Koriyama, Japan, 3\u20135 July 2019, Processing Society of Japan. 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Proceedings of the SIGUCCS \u201923: Proceedings of the 2023 ACM SIGUCCS Annual Conference, Chicago, IL, USA.","DOI":"10.1145\/3539811.3579557"},{"key":"ref_21","unstructured":"Docker Inc. (2026, June 04). Docker Engine. Available online: https:\/\/docs.docker.com\/engine\/."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Smith, J.E., and Nair, R. (2005). Virtual Machines, Morgan Kaufmann. Available online: https:\/\/www.sciencedirect.com\/book\/9781558609105\/virtual-machines.","DOI":"10.1016\/B978-155860910-5\/50009-4"},{"key":"ref_23","unstructured":"Kohnfelder, L., and Garg, P. (2026, June 04). The Threats to Our Products. Microsoft Interface. Available online: https:\/\/shostack.org\/files\/microsoft\/The-Threats-To-Our-Products.docx."},{"key":"ref_24","unstructured":"Shostack, A. (2014). Threat Modeling: Designing for Security, Wiley."},{"key":"ref_25","unstructured":"Apple Inc. (2026, June 04). Mac. 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Available online: https:\/\/www.onamae.com\/."}],"container-title":["Network"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2673-8732\/6\/2\/39\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,6,15]],"date-time":"2026-06-15T06:43:25Z","timestamp":1781505805000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2673-8732\/6\/2\/39"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,6,12]]},"references-count":27,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2026,6]]}},"alternative-id":["network6020039"],"URL":"https:\/\/doi.org\/10.3390\/network6020039","relation":{},"ISSN":["2673-8732"],"issn-type":[{"value":"2673-8732","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,6,12]]}}}